diff --git a/vpi/sdf_lexor.lex b/vpi/sdf_lexor.lex
index 5f39380a9..a653ff53c 100644
--- a/vpi/sdf_lexor.lex
+++ b/vpi/sdf_lexor.lex
@@ -45,6 +45,7 @@ static int yywrap(void)
 %}
 
 %x CCOMMENT
+%x EDGE_ID
 
 %%
 
@@ -62,6 +63,16 @@ static int yywrap(void)
   /* Count lines so that the parser can assign line numbers. */
 \n { sdflloc.first_line += 1; }
 
+  /* The other edge identifiers. */
+<EDGE_ID>"01"    {return K_01; }
+<EDGE_ID>"10"    {return K_10; }
+<EDGE_ID>"0"[zZ] {return K_0Z; }
+<EDGE_ID>[zZ]"1" {return K_Z1; }
+<EDGE_ID>"1"[zZ] {return K_1Z; }
+<EDGE_ID>[zZ]"0" {return K_Z0; }
+<EDGE_ID>[pP][oO][sS][eE][dD][gG][eE] {return K_POSEDGE; }
+<EDGE_ID>[nN][eE][gG][eE][dD][gG][eE] {return K_NEGEDGE; }
+
   /* Real values */
 [0-9]+(\.[0-9]+)?([Ee][+-]?[0-9]+)? {
       yylval.real_val = strtod(yytext, 0);
@@ -107,8 +118,6 @@ static struct {
       { "INTERCONNECT",K_INTERCONNECT },
       { "INSTANCE",   K_INSTANCE },
       { "IOPATH",     K_IOPATH },
-      { "NEGEDGE",    K_NEGEDGE },
-      { "POSEDGE",    K_POSEDGE },
       { "PROCESS",    K_PROCESS },
       { "PROGRAM",    K_PROGRAM },
       { "RECOVERY",   K_RECOVERY },
@@ -126,6 +135,16 @@ static struct {
       { 0, IDENTIFIER }
 };
 
+void start_edge_id(void)
+{
+      BEGIN(EDGE_ID);
+}
+
+void stop_edge_id(void)
+{
+      BEGIN(0);
+}
+
 static int lookup_keyword(const char*text)
 {
       int idx;
diff --git a/vpi/sdf_parse.y b/vpi/sdf_parse.y
index f4859add1..f432ed9e6 100644
--- a/vpi/sdf_parse.y
+++ b/vpi/sdf_parse.y
@@ -48,6 +48,7 @@ char sdf_use_hchar = '.';
 %token K_NEGEDGE K_POSEDGE K_PROCESS K_PROGRAM K_RECOVERY K_REMOVAL
 %token K_SDFVERSION K_SETUP K_SETUPHOLD K_TEMPERATURE K_TIMESCALE
 %token K_TIMINGCHECK K_VENDOR K_VERSION K_VOLTAGE K_WIDTH
+%token K_01 K_10 K_0Z K_Z1 K_1Z K_Z0
 
 %token HCHAR
 %token <string_val> QSTRING IDENTIFIER
@@ -301,13 +302,19 @@ port
   ;
 
 port_edge
-  : '(' edge_identifier port_instance ')'
-      { $$.vpi_edge = $2; $$.string_val = $3; }
+  : '(' {start_edge_id();} edge_identifier {stop_edge_id();} port_instance ')'
+      { $$.vpi_edge = $3; $$.string_val = $5; }
   ;
 
 edge_identifier
   : K_POSEDGE { $$ = vpiPosedge; }
   | K_NEGEDGE { $$ = vpiNegedge; }
+  | K_01      { $$ = vpiEdge01; }
+  | K_10      { $$ = vpiEdge10; }
+  | K_0Z      { $$ = vpiEdge0x; }
+  | K_Z1      { $$ = vpiEdgex1; }
+  | K_1Z      { $$ = vpiEdge1x; }
+  | K_Z0      { $$ = vpiEdgex0; }
   ;
 
 delval_list
diff --git a/vpi/sdf_parse_priv.h b/vpi/sdf_parse_priv.h
index 755bc5405..3483a81f9 100644
--- a/vpi/sdf_parse_priv.h
+++ b/vpi/sdf_parse_priv.h
@@ -1,7 +1,7 @@
 #ifndef _sdf_parse_priv_h
 #define _sdf_parse_priv_h
 /*
- * Copyright (c) 2007 Stephen Williams (steve@icarus.com)
+ * Copyright (c) 2007-2009 Stephen Williams (steve@icarus.com)
  *
  *    This source code is free software; you can redistribute it
  *    and/or modify it in source code form under the terms of the GNU
@@ -35,4 +35,7 @@ extern const char*sdf_parse_path;
 /* Hierarchy separator character to use. */
 extern char sdf_use_hchar;
 
+extern void start_edge_id(void);
+extern void stop_edge_id(void);
+
 #endif
diff --git a/vpi/sys_sdf.c b/vpi/sys_sdf.c
index e89e4943c..cb5861b33 100644
--- a/vpi/sys_sdf.c
+++ b/vpi/sys_sdf.c
@@ -173,6 +173,7 @@ void sdf_iopath_delays(int vpi_edge, const char*src, const char*dst,
 	      /* The edge type must match too. But note that if this
 	         IOPATH has no edge, then it matches with all edges of
 	         the modpath object. */
+/* --> Is this correct in the context of the 10, 01, etc. edges? */
 	    if (vpi_edge != vpiNoEdge && vpi_get(vpiEdge,path_t_in) != vpi_edge)
 		  continue;