diff --git a/src/frontend/inpcom.c b/src/frontend/inpcom.c
index 7fe96e13f..7d02903f1 100644
--- a/src/frontend/inpcom.c
+++ b/src/frontend/inpcom.c
@@ -5617,15 +5617,16 @@ inp_temper_compat(struct card *card)
             modified_exp = inp_modify_exp(exp_str);
             tfree(exp_str);
             /* add the intermediate string between previous and next expression to the new line */
-            new_str = INPstrCat(new_str, copy_substring(beg_str, end_str), " ");
+            new_str = INPstrCat(new_str, ' ',
+                    copy_substring(beg_str, end_str));
             /* add the modified expression string to the new line */
-            new_str = INPstrCat(new_str, modified_exp, " ");
-            new_str = INPstrCat(new_str, copy(" "), " ");
+            new_str = INPstrCat(new_str, ' ', modified_exp);
+            new_str = INPstrCat(new_str, ' ', copy(" "));
             /* move on to the next intermediate string */
             beg_str = beg_tstr = end_tstr;
         }
         if (*beg_str)
-            new_str = INPstrCat(new_str, copy(beg_str), " ");
+            new_str = INPstrCat(new_str, ' ', copy(beg_str));
         tfree(card->line);
         card->line = inp_remove_ws(new_str);
     }
@@ -6230,7 +6231,7 @@ inp_fix_temper_in_param(struct card *deck)
             }
 
             /* restore first part of the line */
-            new_str = INPstrCat(firsttok_str, new_str, " ");
+            new_str = INPstrCat(firsttok_str, ' ', new_str);
             new_str = inp_remove_ws(new_str);
 
             /* if we have inserted into a .param line, convert to .func */
@@ -6448,7 +6449,7 @@ inp_fix_agauss_in_param(struct card *deck, char *fcn)
             }
 
             /* restore first part of the line */
-            new_str = INPstrCat(firsttok_str, new_str, " ");
+            new_str = INPstrCat(firsttok_str, ' ', new_str);
             new_str = inp_remove_ws(new_str);
 
             *card->line = '*';
diff --git a/src/include/ngspice/inpdefs.h b/src/include/ngspice/inpdefs.h
index e5f7b0554..e46c82d3b 100644
--- a/src/include/ngspice/inpdefs.h
+++ b/src/include/ngspice/inpdefs.h
@@ -94,7 +94,7 @@ char *INPdevParse(char **, CKTcircuit *, int, GENinstance *, double *, int *, IN
 char *INPdomodel(CKTcircuit *, struct card *, INPtables *);
 void INPdoOpts(CKTcircuit *, JOB *, struct card *, INPtables *);
 char *INPerrCat(char *, char *);
-char *INPstrCat(char *, char *, char *);
+char *INPstrCat(char *, char, char *);
 char *INPerror(int);
 double INPevaluate(char **, int *, int);
 char *INPfindLev(char *, int *);
diff --git a/src/spicelib/parser/inperrc.c b/src/spicelib/parser/inperrc.c
index b56b51912..cb3077ffe 100644
--- a/src/spicelib/parser/inperrc.c
+++ b/src/spicelib/parser/inperrc.c
@@ -8,50 +8,73 @@ Author: 1985 Thomas L. Quarles
   a new string is malloced, they are combined, both input strings
   are freed, and the new string is returned.
  */
+#include <stdio.h>
+#include <string.h>
 
 #include "ngspice/ngspice.h"
-#include <stdio.h>
 #include "ngspice/inpdefs.h"
 #include "inpxx.h"
 
+static char *INPcat(size_t n_a, const char *a, char sep_char,
+        size_t n_b, const char *b);
 
+
+/* This function returns the non-null string a or b if only one of them
+ * is not null. Otherwise it returns NULL if both are null or
+ * <a>'\n'<b> if both are non-null. */
 char *INPerrCat(char *a, char *b)
 {
-    if (a != NULL) {
-        if (b == NULL) {        /* a valid, b null, return a */
-            return (a);
-        } else {                /* both valid  - hard work... */
-            register char *errtmp;
-            errtmp =
-                TMALLOC(char, strlen(a) + strlen(b) + 2);
-            (void) strcpy(errtmp, a);
-            (void) strcat(errtmp, "\n");
-            (void) strcat(errtmp, b);
-            FREE(a);
-            FREE(b);
-            return (errtmp);
-        }
-    } else                      /* a null, so return b */
-        return (b);
-}
+    return INPstrCat(a, '\n', b);
+} /* end of function INPerrCat */
+
 
 
-char *INPstrCat(char *a, char *b, char *c)
+/* This function returns the non-null string a or b if only one of them
+ * is not null. Otherwise it returns NULL if both are null or
+ * <a><seppchar><b> if both are non-null. */
+char *INPstrCat(char *a, char sepchar, char *b)
 {
     if (a != NULL) {
-        if (b == NULL) {        /* a valid, b null, return a */
-            return (a);
-        } else {                /* both valid  - hard work... */
-            register char *strtmp;
-            strtmp =
-                TMALLOC(char, strlen(a) + strlen(b) + 2);
-            (void) strcpy(strtmp, a);
-            (void) strcat(strtmp, c); /* single character only! */
-            (void) strcat(strtmp, b);
-            FREE(a);
-            FREE(b);
-            return (strtmp);
+        if (b == NULL) { /* a valid, b null, return a */
+            return a;
         }
-    } else                      /* a null, so return b */
-        return (b);
-}
+        else { /* both valid  - hard work... */
+            char *a_ch_b = INPcat(strlen(a), a, sepchar,
+                    strlen(b), b);
+            txfree(a);
+            txfree(b);
+            return a_ch_b;
+        }
+    }
+    else { /* a null, so return b */
+        return b;
+    }
+} /* end of function INPstrCat */
+
+
+
+/* This function concatenates strings a and b with sep_char added
+ * between them. Strings a and b need not be null-terminated. */
+static char *INPcat(size_t n_a, const char *a, char sepchar,
+        size_t n_b, const char *b)
+{
+    char *a_ch_b = TMALLOC(char, n_a + n_b + 2);
+
+    /* Build string. Check not really requied since program exits
+     * if allocation in TMALLOC fails but would be if this behavior
+     * is changed. */
+    if (a_ch_b != (char *) NULL) {
+        char *p_cur = a_ch_b;
+        (void) memcpy(p_cur, a, n_a);
+        p_cur += n_a;
+        *p_cur++ = sepchar;
+        (void) memcpy(p_cur, b, n_b);
+        p_cur += n_b;
+        *p_cur = '\0';
+    }
+
+    return a_ch_b;
+} /* end of function INPcat */
+
+
+