diff --git a/src/frontend/numparam/xpressn.c b/src/frontend/numparam/xpressn.c
index c65bb8646..66db45e11 100644
--- a/src/frontend/numparam/xpressn.c
+++ b/src/frontend/numparam/xpressn.c
@@ -714,7 +714,7 @@ fetchid(SPICE_DSTRINGPTR t, const char *s, const char *s_end)
     {
         c = *s++;
         if (s > s_end)
-            c = '\0';
+            break;
 
         // facts: upcase('\0') == '\0'
         // facts: alfanum('\0') == false