diff --git a/cadpli/cadpli.c b/cadpli/cadpli.c
index 9a75ab7dd..66b213e56 100644
--- a/cadpli/cadpli.c
+++ b/cadpli/cadpli.c
@@ -79,7 +79,7 @@ static void thunker_register(void)
       }
 }
 
-void (*vlog_startup_routines[])() = {
+void (*vlog_startup_routines[])(void) = {
       thunker_register,
       0
 };
diff --git a/driver/cflexor.lex b/driver/cflexor.lex
index 9d50c4c4f..b0ba1a40b 100644
--- a/driver/cflexor.lex
+++ b/driver/cflexor.lex
@@ -247,7 +247,7 @@ void cfreset(FILE*fd, const char*path)
 /*
  * Modern version of flex (>=2.5.9) can clean up the scanner data.
  */
-void destroy_lexor()
+void destroy_lexor(void)
 {
 # ifdef FLEX_SCANNER
 #   if YY_FLEX_MAJOR_VERSION >= 2 && YY_FLEX_MINOR_VERSION >= 5
diff --git a/driver/cfparse_misc.h b/driver/cfparse_misc.h
index c72886b36..9570f5625 100644
--- a/driver/cfparse_misc.h
+++ b/driver/cfparse_misc.h
@@ -38,7 +38,7 @@ int cflex(void);
 int cferror(const char *);
 int cfparse(void);
 void switch_to_command_file(const char *);
-void destroy_lexor();
+void destroy_lexor(void);
 char *current_file;
 
 #endif
diff --git a/driver/main.c b/driver/main.c
index 020ca3033..4093ff0f3 100644
--- a/driver/main.c
+++ b/driver/main.c
@@ -205,7 +205,7 @@ void add_cmd_file(const char* filename)
 }
 
 /* Function to return the top command file name from the FIFO. */
-char *get_cmd_file()
+char *get_cmd_file(void)
 {
       char *filename;
 
@@ -402,7 +402,7 @@ static int t_preprocess_only(void)
  * needed to run the command from the configuration file (which is
  * already parsed for us) so we can handle must of the generic cases.
  */
-static int t_compile()
+static int t_compile(void)
 {
       unsigned rc;
 
diff --git a/ivlpp/globals.h b/ivlpp/globals.h
index db7d660a5..259823468 100644
--- a/ivlpp/globals.h
+++ b/ivlpp/globals.h
@@ -22,11 +22,11 @@
 # include  <stdio.h>
 
 extern void reset_lexor(FILE*out, char*paths[]);
-extern void destroy_lexor();
+extern void destroy_lexor(void);
 extern void load_precompiled_defines(FILE*src);
 extern void define_macro(const char*name, const char*value, int keyword,
                          int argc);
-extern void free_macros();
+extern void free_macros(void);
 extern void dump_precompiled_defines(FILE*out);
 
 /* These variables contain the include directories to be searched when
@@ -54,6 +54,6 @@ extern char dep_mode;
 extern int verbose_flag;
 
 /* This is the entry to the lexer. */
-extern int yylex();
+extern int yylex(void);
 
 #endif
diff --git a/ivlpp/lexor.lex b/ivlpp/lexor.lex
index 9ed6aadff..f7073b58d 100644
--- a/ivlpp/lexor.lex
+++ b/ivlpp/lexor.lex
@@ -30,29 +30,29 @@
 # include  "globals.h"
 # include  "ivl_alloc.h"
 
-static void output_init();
+static void output_init(void);
 #define YY_USER_INIT output_init()
 
-static void  def_start();
-static void  def_add_arg();
-static void  def_finish();
-static void  def_undefine();
-static void  do_define();
-static int   def_is_done();
+static void  def_start(void);
+static void  def_add_arg(void);
+static void  def_finish(void);
+static void  def_undefine(void);
+static void  do_define(void);
+static int   def_is_done(void);
 static int   is_defined(const char*name);
 
 static int   macro_needs_args(const char*name);
-static void  macro_start_args();
+static void  macro_start_args(void);
 static void  macro_add_to_arg(int is_whitespace);
-static void  macro_finish_arg();
+static void  macro_finish_arg(void);
 static void  do_expand(int use_args);
 static const char* do_magic(const char*name);
-static const char* macro_name();
+static const char* macro_name(void);
 
-static void include_filename();
-static void do_include();
+static void include_filename(void);
+static void do_include(void);
 
-static int load_next_input();
+static int load_next_input(void);
 
 struct include_stack_t
 {
@@ -804,7 +804,7 @@ static /* inline */ char* def_argv(int arg)
     return def_buf + def_argo[arg];
 }
 
-static void check_for_max_args()
+static void check_for_max_args(void)
 {
     if (def_argc == MAX_DEF_ARG)
     {
@@ -825,14 +825,14 @@ static void def_buf_grow_to_fit(int length)
     }
 }
 
-static void def_start()
+static void def_start(void)
 {
     def_buf_free = def_buf_size;
     def_argc = 0;
     def_add_arg();
 }
 
-static void def_add_arg()
+static void def_add_arg(void)
 {
     int length = yyleng;
 
@@ -979,7 +979,7 @@ static void free_macro(struct define_t* def)
     free(def);
 }
 
-void free_macros()
+void free_macros(void)
 {
     free_macro(def_table);
 }
@@ -1052,7 +1052,7 @@ static char *find_arg(char*ptr, char*head, char*arg)
  * continuation, then return 1 and this function may be called again
  * to collect another line of the definition.
  */
-static void do_define()
+static void do_define(void)
 {
     char* cp;
     char* head;
@@ -1202,7 +1202,7 @@ static void do_define()
  * Return true if the definition text is done. This is the opposite of
  * the define_continue_flag.
  */
-static int def_is_done()
+static int def_is_done(void)
 {
     return !define_continue_flag;
 }
@@ -1212,7 +1212,7 @@ static int def_is_done()
  * assigned value to the parsed name. If there is no value, then
  * assign the string "" (empty string.)
  */
-static void def_finish()
+static void def_finish(void)
 {
     define_continue_flag = 0;
 
@@ -1234,7 +1234,7 @@ static void def_finish()
     def_argc = 0;
 }
 
-static void def_undefine()
+static void def_undefine(void)
 {
     struct define_t* cur;
     struct define_t* tail;
@@ -1360,7 +1360,7 @@ static int macro_needs_args(const char*text)
     }
 }
 
-static const char* macro_name()
+static const char* macro_name(void)
 {
     return cur_macro ? cur_macro->name : "";
 }
@@ -1402,7 +1402,7 @@ static void macro_add_to_arg(int is_white_space)
     def_buf_free -= length;
 }
 
-static void macro_finish_arg()
+static void macro_finish_arg(void)
 {
     char* tail = &def_buf[def_buf_size - def_buf_free];
 
@@ -1443,7 +1443,7 @@ static void exp_buf_grow_to_fit(int length)
     }
 }
 
-static void expand_using_args()
+static void expand_using_args(void)
 {
     char* head;
     char* tail;
@@ -1687,13 +1687,13 @@ static const char* do_magic(const char*name)
  * parsing resumes.
  */
 
-static void output_init()
+static void output_init(void)
 {
     if (line_direct_flag)
         fprintf(yyout, "`line 1 \"%s\" 0\n", istack->path);
 }
 
-static void include_filename()
+static void include_filename(void)
 {
     if(standby) {
         emit_pathline(istack);
@@ -1712,7 +1712,7 @@ static void include_filename()
     standby->comment = NULL;
 }
 
-static void do_include()
+static void do_include(void)
 {
     /* standby is defined by include_filename() */
     if (standby->path[0] == '/') {
@@ -1835,7 +1835,7 @@ static void emit_pathline(struct include_stack_t* isp)
     fprintf(stderr, "%s:%u: ", isp->path, isp->lineno+1);
 }
 
-static void lexor_done()
+static void lexor_done(void)
 {
     while (ifdef_stack)
     {
@@ -1923,7 +1923,7 @@ static void open_input_file(struct include_stack_t*isp)
  * end of a base file, in which case the next base source file is
  * opened.
  */
-static int load_next_input()
+static int load_next_input(void)
 {
     int line_mask_flag = 0;
     struct include_stack_t* isp = istack;
@@ -2193,7 +2193,7 @@ void reset_lexor(FILE* out, char* paths[])
 /*
  * Modern version of flex (>=2.5.9) can clean up the scanner data.
  */
-void destroy_lexor()
+void destroy_lexor(void)
 {
 # ifdef FLEX_SCANNER
 #   if YY_FLEX_MAJOR_VERSION >= 2 && YY_FLEX_MINOR_VERSION >= 5
diff --git a/tgt-vlog95/logic_lpm.c b/tgt-vlog95/logic_lpm.c
index 3556dba61..2ac5fafc6 100644
--- a/tgt-vlog95/logic_lpm.c
+++ b/tgt-vlog95/logic_lpm.c
@@ -1201,7 +1201,7 @@ static void emit_lpm_as_ca(ivl_scope_t scope, ivl_lpm_t lpm,
       if (sign_type != NO_SIGN) fprintf(vlog_out, ")");
 }
 
-static void emit_posedge_dff_prim()
+static void emit_posedge_dff_prim(void)
 {
       fprintf(vlog_out, "\n");
       fprintf(vlog_out, "/* Icarus generated UDP to represent a synthesized "
diff --git a/tgt-vlog95/stmt.c b/tgt-vlog95/stmt.c
index d5c2c037d..98fae285f 100644
--- a/tgt-vlog95/stmt.c
+++ b/tgt-vlog95/stmt.c
@@ -23,7 +23,7 @@
 
 static unsigned single_indent = 0;
 
-static unsigned get_indent()
+static unsigned get_indent(void)
 {
       if (single_indent) {
 	    single_indent = 0;
diff --git a/tgt-vlog95/vlog95_priv.h b/tgt-vlog95/vlog95_priv.h
index af0fd9c92..db9522642 100644
--- a/tgt-vlog95/vlog95_priv.h
+++ b/tgt-vlog95/vlog95_priv.h
@@ -106,10 +106,10 @@ extern void emit_nexus_as_ca(ivl_scope_t scope, ivl_nexus_t nex,
 extern void emit_nexus_port_driver_as_ca(ivl_scope_t scope, ivl_nexus_t nex);
 extern void emit_const_nexus(ivl_scope_t scope, ivl_net_const_t const_net);
 extern void emit_signal_net_const_as_ca(ivl_scope_t scope, ivl_signal_t sig);
-extern void emit_icarus_generated_udps();
+extern void emit_icarus_generated_udps(void);
 
 extern void add_udp_to_list(ivl_udp_t udp);
-extern void emit_udp_list();
+extern void emit_udp_list(void);
 extern void emit_sig_file_line(ivl_signal_t sig);
 
 extern void emit_id(const char *id);
@@ -148,7 +148,7 @@ extern void get_sig_msb_lsb(ivl_signal_t sig, int *msb, int *lsb);
 /*
  * Cleanup functions.
  */
-extern void free_emitted_scope_list();
+extern void free_emitted_scope_list(void);
 
 /*
  * Debug routine to dump the various pieces of nexus information.
diff --git a/tgt-vvp/draw_net_input.c b/tgt-vvp/draw_net_input.c
index 9b4a2e2af..4a1c345be 100644
--- a/tgt-vvp/draw_net_input.c
+++ b/tgt-vvp/draw_net_input.c
@@ -158,7 +158,7 @@ static char* draw_C8_to_string(ivl_net_const_t cptr,
       return result;
 }
 
-static struct vvp_nexus_data*new_nexus_data()
+static struct vvp_nexus_data*new_nexus_data(void)
 {
       struct vvp_nexus_data*data = calloc(1, sizeof(struct vvp_nexus_data));
       return data;
diff --git a/tgt-vvp/vvp_priv.h b/tgt-vvp/vvp_priv.h
index 40d8d87dc..ef7afe9ba 100644
--- a/tgt-vvp/vvp_priv.h
+++ b/tgt-vvp/vvp_priv.h
@@ -176,7 +176,7 @@ struct vvp_nexus_data {
  * cache it.
  */
 extern const char* draw_net_input(ivl_nexus_t nex);
-void EOC_cleanup_drivers();
+void EOC_cleanup_drivers(void);
 
 /*
  * This is different from draw_net_input in that it is intended to be
diff --git a/vpi/sdf_lexor.lex b/vpi/sdf_lexor.lex
index 17d4eeaa1..0b8c7767e 100644
--- a/vpi/sdf_lexor.lex
+++ b/vpi/sdf_lexor.lex
@@ -213,7 +213,7 @@ static void process_quoted_string(void)
 /*
  * Modern version of flex (>=2.5.9) can clean up the scanner data.
  */
-static void destroy_sdf_lexor()
+static void destroy_sdf_lexor(void)
 {
 # ifdef FLEX_SCANNER
 #   if YY_FLEX_MAJOR_VERSION >= 2 && YY_FLEX_MINOR_VERSION >= 5
diff --git a/vpi/sys_convert.c b/vpi/sys_convert.c
index 01f12013f..1b03408e9 100644
--- a/vpi/sys_convert.c
+++ b/vpi/sys_convert.c
@@ -231,7 +231,7 @@ static PLI_INT32 sys_rtoi_calltf(ICARUS_VPI_CONST PLI_BYTE8*user)
     return 0;
 }
 
-void sys_convert_register()
+void sys_convert_register(void)
 {
       s_vpi_systf_data tf_data;
       vpiHandle res;
diff --git a/vpi/sys_countdrivers.c b/vpi/sys_countdrivers.c
index 417d20b5a..390f4eb56 100644
--- a/vpi/sys_countdrivers.c
+++ b/vpi/sys_countdrivers.c
@@ -196,7 +196,7 @@ args_done:
 /*
  * Routine to register the system tasks/functions provided in this file.
  */
-void sys_countdrivers_register()
+void sys_countdrivers_register(void)
 {
       s_vpi_systf_data tf_data;
       vpiHandle res;
diff --git a/vpi/sys_deposit.c b/vpi/sys_deposit.c
index f2f95f562..a8ad54514 100644
--- a/vpi/sys_deposit.c
+++ b/vpi/sys_deposit.c
@@ -90,7 +90,7 @@ static PLI_INT32 sys_deposit_calltf(ICARUS_VPI_CONST PLI_BYTE8 *name)
       return 0;
 }
 
-void sys_deposit_register()
+void sys_deposit_register(void)
 {
       s_vpi_systf_data tf_data;
       vpiHandle res;
diff --git a/vpi/sys_display.c b/vpi/sys_display.c
index d452d2065..5a5bc9d43 100644
--- a/vpi/sys_display.c
+++ b/vpi/sys_display.c
@@ -2062,7 +2062,7 @@ static PLI_INT32 sys_end_of_simulation(p_cb_data cb_data)
       return 0;
 }
 
-void sys_display_register()
+void sys_display_register(void)
 {
       s_cb_data cb_data;
       s_vpi_systf_data tf_data;
diff --git a/vpi/sys_fileio.c b/vpi/sys_fileio.c
index b503d4f81..ec99c9f00 100644
--- a/vpi/sys_fileio.c
+++ b/vpi/sys_fileio.c
@@ -1056,7 +1056,7 @@ static PLI_INT32 sys_ferror_calltf(ICARUS_VPI_CONST PLI_BYTE8 *name)
       return 0;
 }
 
-void sys_fileio_register()
+void sys_fileio_register(void)
 {
       s_vpi_systf_data tf_data;
       vpiHandle res;
diff --git a/vpi/sys_finish.c b/vpi/sys_finish.c
index 642765621..cc3a88326 100644
--- a/vpi/sys_finish.c
+++ b/vpi/sys_finish.c
@@ -46,7 +46,7 @@ static PLI_INT32 sys_finish_calltf(ICARUS_VPI_CONST PLI_BYTE8 *name)
       return 0;
 }
 
-void sys_finish_register()
+void sys_finish_register(void)
 {
       s_vpi_systf_data tf_data;
       vpiHandle res;
diff --git a/vpi/sys_plusargs.c b/vpi/sys_plusargs.c
index 7f7935aee..357a2d652 100644
--- a/vpi/sys_plusargs.c
+++ b/vpi/sys_plusargs.c
@@ -381,7 +381,7 @@ static PLI_INT32 sys_value_plusargs_calltf(ICARUS_VPI_CONST PLI_BYTE8*name)
       return 0;
 }
 
-void sys_plusargs_register()
+void sys_plusargs_register(void)
 {
       s_vpi_systf_data tf_data;
       vpiHandle res;
diff --git a/vpi/sys_queue.c b/vpi/sys_queue.c
index e0be73d71..7c0972b2e 100644
--- a/vpi/sys_queue.c
+++ b/vpi/sys_queue.c
@@ -1393,7 +1393,7 @@ static PLI_INT32 sys_q_exam_calltf(ICARUS_VPI_CONST PLI_BYTE8 *name)
 /*
  * Routine to register the system tasks/functions provided in this file.
  */
-void sys_queue_register()
+void sys_queue_register(void)
 {
       s_vpi_systf_data tf_data;
       s_cb_data cb;
diff --git a/vpi/sys_random.c b/vpi/sys_random.c
index 78546b64f..bd44c7a70 100644
--- a/vpi/sys_random.c
+++ b/vpi/sys_random.c
@@ -909,7 +909,7 @@ static PLI_INT32 sys_rand_func_sizetf(PLI_BYTE8 *x)
       return 32;
 }
 
-void sys_random_register()
+void sys_random_register(void)
 {
       s_vpi_systf_data tf_data;
       vpiHandle res;
diff --git a/vpi/sys_random_mti.c b/vpi/sys_random_mti.c
index 58753ac85..8a20c6164 100644
--- a/vpi/sys_random_mti.c
+++ b/vpi/sys_random_mti.c
@@ -142,7 +142,7 @@ static PLI_INT32 sys_mti_random_calltf(ICARUS_VPI_CONST PLI_BYTE8*name)
       return 0;
 }
 
-void sys_random_mti_register()
+void sys_random_mti_register(void)
 {
       s_vpi_systf_data tf_data;
       vpiHandle res;
diff --git a/vpi/sys_readmem.c b/vpi/sys_readmem.c
index b35154a03..15170b31a 100644
--- a/vpi/sys_readmem.c
+++ b/vpi/sys_readmem.c
@@ -569,7 +569,7 @@ static PLI_INT32 sys_writemem_calltf(ICARUS_VPI_CONST PLI_BYTE8*name)
       return 0;
 }
 
-void sys_readmem_register()
+void sys_readmem_register(void)
 {
       s_vpi_systf_data tf_data;
       vpiHandle res;
diff --git a/vpi/sys_readmem_lex.h b/vpi/sys_readmem_lex.h
index c638ec6d6..b7e18376a 100644
--- a/vpi/sys_readmem_lex.h
+++ b/vpi/sys_readmem_lex.h
@@ -30,8 +30,8 @@ extern char *readmem_error_token;
 
 extern void sys_readmem_start_file(FILE*in, int bin_flag,
 				   unsigned width, struct t_vpi_vecval*val);
-extern int readmemlex();
+extern int readmemlex(void);
 
-extern void destroy_readmem_lexor();
+extern void destroy_readmem_lexor(void);
 
 #endif
diff --git a/vpi/sys_readmem_lex.lex b/vpi/sys_readmem_lex.lex
index c7b90f9ba..22e5b0e80 100644
--- a/vpi/sys_readmem_lex.lex
+++ b/vpi/sys_readmem_lex.lex
@@ -24,9 +24,9 @@
 
 # include "sys_readmem_lex.h"
 # include  <string.h>
-static void make_addr();
-static void make_hex_value();
-static void make_bin_value();
+static void make_addr(void);
+static void make_hex_value(void);
+static void make_bin_value(void);
 
 static int save_state;
 
@@ -60,12 +60,12 @@ char *readmem_error_token = 0;
 static unsigned word_width = 0;
 static struct t_vpi_vecval*vecval = 0;
 
-static void make_addr()
+static void make_addr(void)
 {
       sscanf(yytext+1, "%x", (unsigned int*)&vecval->aval);
 }
 
-static void make_hex_value()
+static void make_hex_value(void)
 {
       char*beg = yytext;
       char*end = beg + strlen(beg);
@@ -136,7 +136,7 @@ static void make_hex_value()
       }
 }
 
-static void make_bin_value()
+static void make_bin_value(void)
 {
       char*beg = yytext;
       char*end = beg + strlen(beg);
@@ -195,7 +195,7 @@ void sys_readmem_start_file(FILE*in, int bin_flag,
 /*
  * Modern version of flex (>=2.5.9) can clean up the scanner data.
  */
-void destroy_readmem_lexor()
+void destroy_readmem_lexor(void)
 {
 # ifdef FLEX_SCANNER
 #   if YY_FLEX_MAJOR_VERSION >= 2 && YY_FLEX_MINOR_VERSION >= 5
diff --git a/vpi/sys_scanf.c b/vpi/sys_scanf.c
index e400fe947..3e7534cdf 100644
--- a/vpi/sys_scanf.c
+++ b/vpi/sys_scanf.c
@@ -1435,7 +1435,7 @@ static PLI_INT32 sys_sscanf_calltf(ICARUS_VPI_CONST PLI_BYTE8 *name)
       return 0;
 }
 
-void sys_scanf_register()
+void sys_scanf_register(void)
 {
       s_vpi_systf_data tf_data;
       vpiHandle res;
diff --git a/vpi/sys_sdf.c b/vpi/sys_sdf.c
index 2ee6c1fe1..5d69ff623 100644
--- a/vpi/sys_sdf.c
+++ b/vpi/sys_sdf.c
@@ -318,7 +318,7 @@ static PLI_INT32 sys_sdf_annotate_calltf(ICARUS_VPI_CONST PLI_BYTE8*name)
       return 0;
 }
 
-void sys_sdf_register()
+void sys_sdf_register(void)
 {
       s_vpi_systf_data tf_data;
       vpiHandle res;
diff --git a/vpi/sys_table.c b/vpi/sys_table.c
index 6e9a4326c..bb5e3ad7e 100644
--- a/vpi/sys_table.c
+++ b/vpi/sys_table.c
@@ -23,42 +23,42 @@
 # include <stdlib.h>
 # include <string.h>
 
-extern void sys_convert_register();
-extern void sys_countdrivers_register();
-extern void sys_darray_register();
-extern void sys_fileio_register();
-extern void sys_finish_register();
-extern void sys_deposit_register();
-extern void sys_display_register();
-extern void sys_plusargs_register();
-extern void sys_queue_register();
-extern void sys_random_register();
-extern void sys_random_mti_register();
-extern void sys_readmem_register();
-extern void sys_scanf_register();
-extern void sys_sdf_register();
-extern void sys_time_register();
-extern void sys_vcd_register();
-extern void sys_vcdoff_register();
-extern void sys_special_register();
-extern void table_model_register();
-extern void vams_simparam_register();
+extern void sys_convert_register(void);
+extern void sys_countdrivers_register(void);
+extern void sys_darray_register(void);
+extern void sys_fileio_register(void);
+extern void sys_finish_register(void);
+extern void sys_deposit_register(void);
+extern void sys_display_register(void);
+extern void sys_plusargs_register(void);
+extern void sys_queue_register(void);
+extern void sys_random_register(void);
+extern void sys_random_mti_register(void);
+extern void sys_readmem_register(void);
+extern void sys_scanf_register(void);
+extern void sys_sdf_register(void);
+extern void sys_time_register(void);
+extern void sys_vcd_register(void);
+extern void sys_vcdoff_register(void);
+extern void sys_special_register(void);
+extern void table_model_register(void);
+extern void vams_simparam_register(void);
 
 #ifdef HAVE_LIBZ
 #ifdef HAVE_LIBBZ2
-extern void sys_lxt_register();
+extern void sys_lxt_register(void);
 #else
-static void sys_lxt_register() { fputs("LXT support disabled since libbzip2 not available\n",stderr); exit(1); }
+static void sys_lxt_register(void) { fputs("LXT support disabled since libbzip2 not available\n",stderr); exit(1); }
 #endif
-extern void sys_lxt2_register();
-extern void sys_fst_register();
+extern void sys_lxt2_register(void);
+extern void sys_fst_register(void);
 #else
-static void sys_lxt_register() { fputs("LXT support disabled since zlib not available\n",stderr); exit(1); }
-static void sys_lxt2_register() { fputs("LXT2 support disabled since zlib not available\n",stderr); exit(1); }
-static void sys_fst_register() { fputs("FST support disabled since zlib not available\n",stderr); exit(1); }
+static void sys_lxt_register(void) { fputs("LXT support disabled since zlib not available\n",stderr); exit(1); }
+static void sys_lxt2_register(void) { fputs("LXT2 support disabled since zlib not available\n",stderr); exit(1); }
+static void sys_fst_register(void) { fputs("FST support disabled since zlib not available\n",stderr); exit(1); }
 #endif
 
-static void sys_lxt_or_vcd_register()
+static void sys_lxt_or_vcd_register(void)
 {
       int idx;
       struct t_vpi_vlog_info vlog_info;
@@ -195,7 +195,7 @@ static void sys_lxt_or_vcd_register()
       }
 }
 
-void (*vlog_startup_routines[])() = {
+void (*vlog_startup_routines[])(void) = {
       sys_convert_register,
       sys_countdrivers_register,
       sys_darray_register,
diff --git a/vpi/sys_time.c b/vpi/sys_time.c
index e904d2718..18f248a4e 100644
--- a/vpi/sys_time.c
+++ b/vpi/sys_time.c
@@ -107,7 +107,7 @@ static PLI_INT32 sys_realtime_calltf(ICARUS_VPI_CONST PLI_BYTE8*name)
       return 0;
 }
 
-void sys_time_register()
+void sys_time_register(void)
 {
       s_vpi_systf_data tf_data;
       vpiHandle res;
diff --git a/vpi/sys_vcd.c b/vpi/sys_vcd.c
index 62a6f75b5..ea4ccb7b2 100644
--- a/vpi/sys_vcd.c
+++ b/vpi/sys_vcd.c
@@ -159,7 +159,7 @@ __inline__ static int dump_header_pending(void)
  * This function writes out all the traced variables, whether they
  * changed or not.
  */
-static void vcd_checkpoint()
+static void vcd_checkpoint(void)
 {
       struct vcd_info*cur;
 
@@ -167,7 +167,7 @@ static void vcd_checkpoint()
 	    show_this_item(cur);
 }
 
-static void vcd_checkpoint_x()
+static void vcd_checkpoint_x(void)
 {
       struct vcd_info*cur;
 
@@ -855,7 +855,7 @@ static PLI_INT32 sys_dumpvars_calltf(ICARUS_VPI_CONST PLI_BYTE8*name)
       return 0;
 }
 
-void sys_vcd_register()
+void sys_vcd_register(void)
 {
       s_vpi_systf_data tf_data;
       vpiHandle res;
diff --git a/vpi/sys_vcdoff.c b/vpi/sys_vcdoff.c
index 1ce71f709..1c487a864 100644
--- a/vpi/sys_vcdoff.c
+++ b/vpi/sys_vcdoff.c
@@ -48,7 +48,7 @@ static PLI_INT32 sys_dumpvars_calltf(ICARUS_VPI_CONST PLI_BYTE8*name)
       return 0;
 }
 
-void sys_vcdoff_register()
+void sys_vcdoff_register(void)
 {
       s_vpi_systf_data tf_data;
       vpiHandle res;
diff --git a/vpi/table_mod.c b/vpi/table_mod.c
index 9a3c00416..34d23862a 100644
--- a/vpi/table_mod.c
+++ b/vpi/table_mod.c
@@ -64,7 +64,7 @@ static PLI_INT32 cleanup_table_mod(p_cb_data cause)
  * Create an empty table model object and add it to the list of table
  * model objects.
  */
-static p_table_mod create_table()
+static p_table_mod create_table(void)
 {
 	/* Create an empty table model object. */
       p_table_mod obj = (p_table_mod) malloc(sizeof(s_table_mod));
@@ -110,7 +110,7 @@ unsigned is_const_string_obj(vpiHandle arg)
 /*
  * Get any command line flags. For now we only have a debug flag.
  */
-static void check_command_line_flags()
+static void check_command_line_flags(void)
 {
       struct t_vpi_vlog_info vlog_info;
       static unsigned command_line_processed = 0;
@@ -684,7 +684,7 @@ static PLI_INT32 sys_table_model_calltf(ICARUS_VPI_CONST PLI_BYTE8 *name)
 /*
  * Routine to register the system function provided in this file.
  */
-void table_model_register()
+void table_model_register(void)
 {
       s_vpi_systf_data tf_data;
       s_cb_data cb;
diff --git a/vpi/table_mod.h b/vpi/table_mod.h
index 35a513404..e1215dfa9 100644
--- a/vpi/table_mod.h
+++ b/vpi/table_mod.h
@@ -94,8 +94,8 @@ typedef struct t_table_mod {
 
 extern unsigned parse_table_model(FILE *fp, vpiHandle callh, p_table_mod table);
 
-extern int tblmodlex();
-extern void destroy_tblmod_lexor();
+extern int tblmodlex(void);
+extern void destroy_tblmod_lexor(void);
 extern void init_tblmod_lexor(FILE *fp);
 
 #endif
diff --git a/vpi/table_mod_lexor.lex b/vpi/table_mod_lexor.lex
index 738c644fe..bd518ee7e 100644
--- a/vpi/table_mod_lexor.lex
+++ b/vpi/table_mod_lexor.lex
@@ -150,7 +150,7 @@ void init_tblmod_lexor(FILE *fp)
 /*
  * Modern version of flex (>=2.5.9) can clean up the scanner data.
  */
-void destroy_tblmod_lexor()
+void destroy_tblmod_lexor(void)
 {
 # ifdef FLEX_SCANNER
 #   if YY_FLEX_MAJOR_VERSION >= 2 && YY_FLEX_MINOR_VERSION >= 5
diff --git a/vpi/table_mod_parse.y b/vpi/table_mod_parse.y
index fb1ff4f18..c1f5f6c25 100644
--- a/vpi/table_mod_parse.y
+++ b/vpi/table_mod_parse.y
@@ -90,7 +90,7 @@ static p_table_mod table_def;
 extern int tblmodlex(void);
 static void yyerror(const char *fmt, ...);
 
-static void process_point()
+static void process_point(void)
 {
       assert(cur_value == indep_values);
   #if 0
diff --git a/vpi/v2005_math.c b/vpi/v2005_math.c
index 4306faccf..ab8fabf2e 100644
--- a/vpi/v2005_math.c
+++ b/vpi/v2005_math.c
@@ -371,7 +371,7 @@ static void sys_v2005_math_register(void)
 /*
  * Hook to get Icarus Verilog to find the registration function.
  */
-extern void sys_clog2_register();
+extern void sys_clog2_register(void);
 
 void (*vlog_startup_routines[])(void) = {
     sys_v2005_math_register,
diff --git a/vpi/v2009_table.c b/vpi/v2009_table.c
index 1b1b3d226..4e3328779 100644
--- a/vpi/v2009_table.c
+++ b/vpi/v2009_table.c
@@ -21,7 +21,7 @@ extern void v2009_array_register(void);
 extern void v2009_enum_register(void);
 extern void v2009_string_register(void);
 
-void (*vlog_startup_routines[])() = {
+void (*vlog_startup_routines[])(void) = {
       v2009_array_register,
       v2009_enum_register,
       v2009_string_register,
diff --git a/vpi/vcd_priv.h b/vpi/vcd_priv.h
index ea96642b3..5c3219648 100644
--- a/vpi/vcd_priv.h
+++ b/vpi/vcd_priv.h
@@ -45,7 +45,7 @@ EXTERN const char *vcd_names_search(struct vcd_names_list_s*tab,
 
 EXTERN void vcd_names_sort(struct vcd_names_list_s*tab);
 
-EXTERN void vcd_names_delete();
+EXTERN void vcd_names_delete(struct vcd_names_list_s*tab);
 
 /*
  * Keep a map of nexus ident's to help with alias detection.
@@ -53,7 +53,7 @@ EXTERN void vcd_names_delete();
 EXTERN const char*find_nexus_ident(int nex);
 EXTERN void       set_nexus_ident(int nex, const char *id);
 
-EXTERN void nexus_ident_delete();
+EXTERN void nexus_ident_delete(void);
 
 /*
  * Keep a set of scope names to help with duplicate detection.
diff --git a/vpi/vhdl_table.c b/vpi/vhdl_table.c
index 4e80e1444..764a18c97 100644
--- a/vpi/vhdl_table.c
+++ b/vpi/vhdl_table.c
@@ -182,7 +182,7 @@ static void vhdl_register(void)
       vpi_register_cb(&cb);
 }
 
-void (*vlog_startup_routines[])() = {
+void (*vlog_startup_routines[])(void) = {
       vhdl_register,
       0
 };
diff --git a/vpi/vpi_debug.c b/vpi/vpi_debug.c
index 4a4515b43..495648ab4 100644
--- a/vpi/vpi_debug.c
+++ b/vpi/vpi_debug.c
@@ -93,7 +93,7 @@ static PLI_INT32 vpi_tree_calltf(ICARUS_VPI_CONST PLI_BYTE8*name)
       return 0;
 }
 
-void sys_register()
+void sys_register(void)
 {
       s_vpi_systf_data tf_data;
       vpiHandle res;
@@ -108,7 +108,7 @@ void sys_register()
       vpip_make_systf_system_defined(res);
 }
 
-void (*vlog_startup_routines[])() = {
+void (*vlog_startup_routines[])(void) = {
       sys_register,
       0
 };
diff --git a/vvp/draw_tt.c b/vvp/draw_tt.c
index d969012f0..10a5da89d 100644
--- a/vvp/draw_tt.c
+++ b/vvp/draw_tt.c
@@ -25,7 +25,7 @@
  * map of a 4-vbit value to a hex digit. The table handles the display
  * of x, X, z, Z, etc.
  */
-static void draw_hex_table()
+static void draw_hex_table(void)
 {
       unsigned idx;
 
@@ -71,7 +71,7 @@ static void draw_hex_table()
       printf("};\n");
 }
 
-static void draw_oct_table()
+static void draw_oct_table(void)
 {
       unsigned idx;
 
@@ -117,7 +117,7 @@ static void draw_oct_table()
       printf("};\n");
 }
 
-int main()
+int main(void)
 {
       draw_hex_table();
       draw_oct_table();
diff --git a/vvp/libvpi.c b/vvp/libvpi.c
index 30ff2eaa4..df6388f17 100644
--- a/vvp/libvpi.c
+++ b/vvp/libvpi.c
@@ -21,6 +21,6 @@
  * Things that should be statically linked by VPI modules go here.
  */
 
-void __libvpi_c_dummy_function()
+void __libvpi_c_dummy_function(void)
 {
 }