diff --git a/src/userfunc.c b/src/userfunc.c
index b9fb644..f7ad9f3 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -1834,6 +1834,22 @@
 }
 
 /*
+ * Check the argument count for user function "fp".
+ * Return FCERR_UNKNOWN if OK, FCERR_TOOFEW or FCERR_TOOMANY otherwise.
+ */
+    int
+check_user_func_argcount(ufunc_T *fp, int argcount)
+{
+    int regular_args = fp->uf_args.ga_len;
+
+    if (argcount < regular_args - fp->uf_def_args.ga_len)
+	return FCERR_TOOFEW;
+    else if (!has_varargs(fp) && argcount > regular_args)
+	return FCERR_TOOMANY;
+    return FCERR_UNKNOWN;
+}
+
+/*
  * Call a user function after checking the arguments.
  */
     int
@@ -1846,15 +1862,13 @@
 	dict_T	    *selfdict)
 {
     int error;
-    int regular_args = fp->uf_args.ga_len;
 
     if (fp->uf_flags & FC_RANGE && funcexe->doesrange != NULL)
 	*funcexe->doesrange = TRUE;
-    if (argcount < regular_args - fp->uf_def_args.ga_len)
-	error = FCERR_TOOFEW;
-    else if (!has_varargs(fp) && argcount > regular_args)
-	error = FCERR_TOOMANY;
-    else if ((fp->uf_flags & FC_DICT) && selfdict == NULL)
+    error = check_user_func_argcount(fp, argcount);
+    if (error != FCERR_UNKNOWN)
+	return error;
+    if ((fp->uf_flags & FC_DICT) && selfdict == NULL)
 	error = FCERR_DICT;
     else
     {