diff --git a/source/compiler/sc1.c b/source/compiler/sc1.c
index 90eaaa7..88d2c0b 100644
--- a/source/compiler/sc1.c
+++ b/source/compiler/sc1.c
@@ -5010,8 +5010,9 @@ static void destructsymbols(symbol *root,int level)
         if ((opsym->usage & uMISSING)!=0 || (opsym->usage & uPROTOTYPED)==0) {
           char symname[2*sNAMEMAX+16];  /* allow space for user defined operators */
           funcdisplayname(symname,opsym->name);
+          char *ptr= (sym->documentation!=NULL) ? sym->documentation : "";
           if ((opsym->usage & uMISSING)!=0)
-            error(4,symname);           /* function not defined */
+            error(4,symname,ptr);       /* function not defined */
           if ((opsym->usage & uPROTOTYPED)==0)
             error(71,symname);          /* operator must be declared before use */
         } /* if */
diff --git a/source/compiler/sc3.c b/source/compiler/sc3.c
index 1185bcb..cf04eab 100644
--- a/source/compiler/sc3.c
+++ b/source/compiler/sc3.c
@@ -195,8 +195,9 @@ static void (*unopers[])(void) = { lneg, neg, user_inc, user_dec };
   if ((sym->usage & uMISSING)!=0 || (sym->usage & uPROTOTYPED)==0) {
     char symname[2*sNAMEMAX+16];  /* allow space for user defined operators */
     funcdisplayname(symname,sym->name);
+    char *ptr= (sym->documentation!=NULL) ? sym->documentation : "";
     if ((sym->usage & uMISSING)!=0)
-      error(4,symname);           /* function not defined */
+      error(4,symname,ptr);       /* function not defined */
     if ((sym->usage & uPROTOTYPED)==0)
       error(71,symname);          /* operator must be declared before use */
   } /* if */
@@ -1880,7 +1881,8 @@ restart:
       } else if ((sym->usage & uMISSING)!=0) {
         char symname[2*sNAMEMAX+16];  /* allow space for user defined operators */
         funcdisplayname(symname,sym->name);
-        error(4,symname);             /* function not defined */
+        char *ptr= (sym->documentation!=NULL) ? sym->documentation : "";
+        error(4,symname,ptr);         /* function not defined */
       } /* if */
       callfunction(sym,lval1,TRUE);
       return FALSE;             /* result of function call is no lvalue */
diff --git a/source/compiler/sc5.c b/source/compiler/sc5.c
index df567f9..ec2d9cb 100644
--- a/source/compiler/sc5.c
+++ b/source/compiler/sc5.c
@@ -43,7 +43,7 @@ static char *errmsg[] = {
 /*001*/  "expected token: \"%s\", but found \"%s\"\n",
 /*002*/  "only a single statement (or expression) can follow each \"case\"\n",
 /*003*/  "declaration of a local variable must appear in a compound block\n",
-/*004*/  "function \"%s\" is not implemented\n",
+/*004*/  "function \"%s\" is not implemented %s\n",
 /*005*/  "function may not have arguments\n",
 /*006*/  "must be assigned to an array\n",
 /*007*/  "operator cannot be redefined\n",