diff --git a/src/frontend/numparam/xpressn.c b/src/frontend/numparam/xpressn.c
index 1bb9e4706..6325dca54 100644
--- a/src/frontend/numparam/xpressn.c
+++ b/src/frontend/numparam/xpressn.c
@@ -1321,7 +1321,7 @@ getword(const char *s, const char * const s_end, SPICE_DSTRINGPTR tstr_p)
 /* isolate a word from s after position "after". return i= last read+1 */
 {
     s++;
-    while ((s < s_end) && !alfa(s[-1]))
+    while ((s-1 < s_end - 1) && !alfa(s[-1]))
         s++;
 
     spice_dstring_reinit(tstr_p);