diff --git a/configure.ac b/configure.ac
index c3c4a4898..47ecc9827 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1180,6 +1180,7 @@ AC_CONFIG_FILES([Makefile
                  tests/regression/subckt-processing/Makefile
                  tests/regression/lib-processing/Makefile
                  tests/regression/parser/Makefile
+                 tests/regression/func/Makefile
                  tests/sensitivity/Makefile
                  tests/transient/Makefile
                  tests/transmission/Makefile
diff --git a/src/frontend/inpcom.c b/src/frontend/inpcom.c
index f6c23cf11..025ee3a6f 100644
--- a/src/frontend/inpcom.c
+++ b/src/frontend/inpcom.c
@@ -75,6 +75,7 @@ struct function_env
         char *macro;
         char *params[N_PARAMS];
         int   num_parameters;
+        const char *accept;
     } *functions;
 };
 
@@ -2888,6 +2889,17 @@ inp_get_func_from_line(struct function_env *env, char *line)
     temp_buf[str_len++] = '\0';
 
     function->macro = strdup(temp_buf);
+
+    {
+        int i;
+
+        char *accept = TMALLOC(char, function->num_parameters + 1);
+        for (i = 0; i < function->num_parameters; i++)
+            accept[i] = function->params[i][0];
+        accept[i] = '\0';
+
+        function->accept = accept;
+    }
 }
 
 
@@ -2925,115 +2937,100 @@ inp_grab_func(struct function_env *env, struct line *c)
 
 
 static char*
-inp_do_macro_param_replace(struct function *fcn, char *params[])
+search_func_arg(char *str, struct function *fcn, int *which, char *str_begin)
 {
-    char *param_ptr, *curr_ptr, *new_str, *curr_str = NULL, *search_ptr;
-    char keep, before, after;
-    int  i;
+    for (; (str = strpbrk(str, fcn->accept)) != NULL; str++) {
+        char before;
 
-    if (fcn->num_parameters == 0)
-        return strdup(fcn->macro);
+        if (str > str_begin)
+            before = str[-1];
+        else
+            before = '\0';
 
-    for (i = 0; i < fcn->num_parameters; i++) {
-
-        if (curr_str == NULL) {
-            search_ptr = curr_ptr = strdup(fcn->macro);
-        } else {
-            search_ptr = curr_ptr = curr_str;
-            curr_str = NULL;
-        }
-
-        while ((param_ptr = strstr(search_ptr, fcn->params[i])) != NULL) {
-            char *op_ptr = NULL, *cp_ptr = NULL;
-            int is_vi = 0;
-
-            /* make sure actually have the parameter name */
-            if (param_ptr == search_ptr) /* no valid 'before' */
-                before = '\0';
-            else
-                before = *(param_ptr-1);
-            after  = param_ptr [ strlen(fcn->params[i]) ];
-            if (!(is_arith_char(before) || isspace(before) ||
-                  before == ',' || before == '=' || (param_ptr-1) < curr_ptr) ||
-                !(is_arith_char(after) || isspace(after) ||
-                  after == ',' || after  == '=' || after  == '\0'))
-            {
-                search_ptr = param_ptr + 1;
-                continue;
-            }
-
-            /* exclude v(nn, parameter), v(parameter, nn), v(parameter),
-            and i(parameter) if here 'parameter' is also a node name */
-            if (before != '\0') {
-                /* go backwards from 'parameter' and find '(' */
-                for (op_ptr = param_ptr-1; op_ptr > curr_ptr; op_ptr--) {
-                    if (*op_ptr == ')') {
-                        is_vi = 0;
-                        break;
-                    }
-                    if ((*op_ptr == '(') && (op_ptr - 2 > curr_ptr) &&
-                       ((*(op_ptr - 1) == 'v') || (*(op_ptr - 1) == 'i')) &&
-                       (is_arith_char(*(op_ptr - 2)) || isspace(*(op_ptr - 2)) ||
-                       *(op_ptr - 2) == ',' || *(op_ptr - 2) == '=' )) {
-                        is_vi = 1;
-                        break;
+        if (is_arith_char(before) || isspace(before) || strchr(",=", before)) {
+            int i;
+            for (i = 0; i < fcn->num_parameters; i++) {
+                size_t len = strlen(fcn->params[i]);
+                if (strncmp(str, fcn->params[i], len) == 0) {
+                    char after = str[len];
+                    if (is_arith_char(after) || isspace(after) || strchr(",=", after)) {
+                        *which = i;
+                        return str;
                     }
                 }
-                /* We have a true v( or i( */
-                if (is_vi) {
-                    cp_ptr = param_ptr;
-                    /* go forward and find closing ')' */
-                    while (*cp_ptr) {
-                       cp_ptr++;
-                       if (*cp_ptr == '(') {
-                           is_vi = 0;
-                           break;
-                       }
-                       if (*cp_ptr == ')')
-                           break;
-                    }
-                    if (*cp_ptr == '\0')
-                        is_vi = 0;
-                }
-                /* We have a true v(...) or i(...),
-                   so skip it, and continue searching for new 'parameter' */
-                if (is_vi) {
-                    search_ptr = cp_ptr;
-                    continue;
-                }
-            }
-
-            keep       = *param_ptr;
-            *param_ptr = '\0';
-
-            {
-                size_t curr_str_len = curr_str ? strlen(curr_str) : 0;
-                size_t len = strlen(curr_ptr) + strlen(params[i]) + 1;
-                if (str_has_arith_char(params[i])) {
-                    curr_str = TREALLOC(char, curr_str, curr_str_len + len + 2);
-                    sprintf(curr_str + curr_str_len, "%s(%s)", curr_ptr, params[i]);
-                } else {
-                    curr_str = TREALLOC(char, curr_str, curr_str_len + len);
-                    sprintf(curr_str + curr_str_len, "%s%s", curr_ptr, params[i]);
-                }
-            }
-
-            *param_ptr = keep;
-            search_ptr = curr_ptr = param_ptr + strlen(fcn->params[i]);
-        }
-
-        if (param_ptr == NULL) {
-            if (curr_str == NULL) {
-                curr_str = curr_ptr;
-            } else {
-                new_str = tprintf("%s%s", curr_str, curr_ptr);
-                tfree(curr_str);
-                curr_str = new_str;
             }
         }
     }
 
-    return curr_str;
+    return NULL;
+}
+
+
+static char*
+inp_do_macro_param_replace(struct function *fcn, char *params[])
+{
+    char *str = strdup(fcn->macro);
+    int  i;
+
+    char *collect_ptr = NULL;
+    char *arg_ptr = str;
+    char *rest = str;
+
+    while ((arg_ptr = search_func_arg(arg_ptr, fcn, &i, str)) != NULL) {
+        char *p;
+        int is_vi = 0;
+
+        /* exclude v(nn, parameter), v(parameter, nn), v(parameter),
+           and i(parameter) if here 'parameter' is also a node name */
+
+        /* go backwards from 'parameter' and find '(' */
+        for (p = arg_ptr; --p > str; )
+            if (*p == '(' || *p == ')') {
+                if ((*p == '(') && strchr("vi", p[-1]) &&
+                    (p - 2 < str || is_arith_char(p[-2]) || isspace(p[-2]) || strchr(",=", p[-2])))
+                    is_vi = 1;
+                break;
+            }
+
+        /* if we have a true v( or i( */
+        if (is_vi) {
+            /* go forward and find closing ')' */
+            for (p = arg_ptr + 1; *p; p++)
+                if (*p == '(' || *p == ')')
+                    break;
+            /* We have a true v(...) or i(...),
+               so skip it, and continue searching for new 'parameter' */
+            if (*p == ')') {
+                arg_ptr = p;
+                continue;
+            }
+        }
+
+        {
+            size_t collect_ptr_len = collect_ptr ? strlen(collect_ptr) : 0;
+            size_t len = strlen(rest) + strlen(params[i]) + 1;
+            int prefix_len = (int) (arg_ptr - rest);
+            if (str_has_arith_char(params[i])) {
+                collect_ptr = TREALLOC(char, collect_ptr, collect_ptr_len + len + 2);
+                sprintf(collect_ptr + collect_ptr_len, "%.*s(%s)", prefix_len, rest, params[i]);
+            } else {
+                collect_ptr = TREALLOC(char, collect_ptr, collect_ptr_len + len);
+                sprintf(collect_ptr + collect_ptr_len, "%.*s%s", prefix_len, rest, params[i]);
+            }
+        }
+
+        arg_ptr += strlen(fcn->params[i]);
+        rest = arg_ptr;
+    }
+
+    if (collect_ptr) {
+        char *new_str = tprintf("%s%s", collect_ptr, rest);
+        tfree(collect_ptr);
+        tfree(str);
+        str = new_str;
+    }
+
+    return str;
 }
 
 
diff --git a/src/misc/string.c b/src/misc/string.c
index 6035c8d95..44ef01f92 100644
--- a/src/misc/string.c
+++ b/src/misc/string.c
@@ -647,8 +647,7 @@ isquote( char ch )
 bool
 is_arith_char( char c )
 {
-  if ( c == '+' || c == '-' || c == '*' || c == '/' || c == '(' || c == ')' || c == '<' ||
-       c == '>' || c == '?' || c == '|' || c == '&' || c == '^')
+  if (c != '\0' && strchr("+-*/()<>?:|&^!%\\", c))
     return TRUE;
   else
     return FALSE;
diff --git a/tests/regression/Makefile.am b/tests/regression/Makefile.am
index 9fd1a3d71..41efde2c8 100644
--- a/tests/regression/Makefile.am
+++ b/tests/regression/Makefile.am
@@ -1,5 +1,5 @@
 ## Process this file with automake to produce Makefile.in
 
-SUBDIRS = lib-processing parser subckt-processing
+SUBDIRS = lib-processing parser subckt-processing func
 
 MAINTAINERCLEANFILES = Makefile.in
diff --git a/tests/regression/func/Makefile.am b/tests/regression/func/Makefile.am
new file mode 100644
index 000000000..900784d41
--- /dev/null
+++ b/tests/regression/func/Makefile.am
@@ -0,0 +1,12 @@
+## Process this file with automake to produce Makefile.in
+
+
+TESTS = func-1.cir
+
+TESTS_ENVIRONMENT = ngspice_vpath=$(srcdir) $(SHELL) $(top_srcdir)/tests/bin/check.sh $(top_builddir)/src/ngspice
+
+EXTRA_DIST = \
+	$(TESTS) \
+	$(TESTS:.cir=.out)
+
+MAINTAINERCLEANFILES = Makefile.in
diff --git a/tests/regression/func/func-1.cir b/tests/regression/func/func-1.cir
new file mode 100644
index 000000000..25f3982e6
--- /dev/null
+++ b/tests/regression/func/func-1.cir
@@ -0,0 +1,124 @@
+* 'func-1' check .func processing
+
+* (exec-spice "ngspice -b %s")
+* (tests-aux-renumber)
+
+
+* ----------------------------------------
+*   introduce some nodenames and instancenames
+*     intentionally meant to collide with parameter names
+
+vncol1  n 0  101.0
+vncol2  p 0  102.0
+vncol3  x 0  103.0
+
+vp  1 0  105.0
+rp  1 0  1.0
+
+* ----------------------------------------
+* arbitrary tests
+
+.func foo0()  '1013.0'
+
+v1001_t  n1001_t 0  '100*foo0()'
+v1001_g  n1001_g 0  '101300.0'
+
+.func bar1(p) 'p'
+
+v1002_t  n1002_t 0  'bar1(117.0)'
+v1003_t  n1003_t 0  '2*bar1(117.0+2.0)'
+
+v1002_g  n1002_g 0  '117.0'
+v1003_g  n1003_g 0  '238.0'
+
+.func bar2(p) 'v(p)+p'
+
+b1004_t  n1004_t 0  v = 'bar2(17.0)'
+v1004_g  n1004_g 0  '119.0'
+
+.func bar3(p) 'p+v(p)'
+
+b1005_t  n1005_t 0  v = 'bar3(17.0)'
+v1005_g  n1005_g 0  '119.0'
+
+.func bar4(p) 'p+v(p)+p'
+
+b1006_t  n1006_t 0  v = 'bar4(17.0)'
+v1006_g  n1006_g 0  '136.0'
+
+.func baz1(n,vp) 'n+i(vp)+vp'
+
+b1007_t  n1007_t 0  v = 'baz1(17.0,10000)'
+v1007_g  n1007_g 0  '9912'
+
+.func baz2(p,n)  'v(p)+p+v(n)'
+
+b1008_t  n1008_t 0  v = 'baz2(1000.0,1e20)'
+v1008_g  n1008_g 0  '1203.0'
+
+.func baz3(x)  'x+x'
+
+v1009_t  n1009_t 0  '17*baz3(100.0)'
+v1009_g  n1009_g 0  '3400.0'
+
+.func moo1(x,p,n) 'x<p?p:n'
+v1010_t  n1010_t 0  '10*moo1(2,3,5)'
+v1010_g  n1010_g 0  '30'
+
+v1011_t  n1011_t 0  '10*moo1(4,3,5)'
+v1011_g  n1011_g 0  '50'
+
+.func moo2(x,p,n) 'x<p?p:x>n?n:x'
+v1012_t  n1012_t 0  '10*moo2(4,3,5)*100'
+v1012_g  n1012_g 0  '4000'
+
+v1013_t  n1013_t 0  '10*moo2(2,3,5)*100'
+v1013_g  n1013_g 0  '3000'
+
+v1014_t  n1014_t 0  '10*moo2(6,3,5)*100'
+v1014_g  n1014_g 0  '5000'
+
+* ----------------------------------------
+
+.param xoo = 100
+.func fun1(a, xoo) 'a*xoo'
+
+v1015_t  n1015_t 0  'fun1(xoo,2)'
+v1015_g  n1015_g 0  '200'
+
+* ----------------------------------------
+
+.control
+
+define mismatch(a,b,err) abs(a-b)>err
+
+op
+
+let total_count = 0
+let fail_count = 0
+
+let tests = 1001 + vector(15)
+
+foreach n $&tests
+  set n_test = "n{$n}_t"
+  set n_gold = "n{$n}_g"
+  if mismatch(v($n_test), v($n_gold), 1e-9)
+    let v_test = v($n_test)
+    let v_gold = v($n_gold)
+    echo "ERROR, test failure, v($n_test) = $&v_test but should be $&v_gold"
+    let fail_count = fail_count + 1
+  end
+  let total_count = total_count + 1
+end
+
+if fail_count > 0
+  echo "ERROR: $&fail_count of $&total_count tests failed"
+  quit 1
+else
+  echo "INFO: $&fail_count of $&total_count tests failed"
+  quit 0
+end
+
+.endc
+
+.end
diff --git a/tests/regression/func/func-1.out b/tests/regression/func/func-1.out
new file mode 100644
index 000000000..4f6a2ad23
--- /dev/null
+++ b/tests/regression/func/func-1.out
@@ -0,0 +1,9 @@
+
+Circuit: * 'xpressn-1' check xpressn.c parser
+
+Doing analysis at TEMP = 27.000000 and TNOM = 27.000000
+
+
+
+No. of Data Rows : 1
+INFO: 0 of 15 tests failed