diff --git a/src/strcasestr.c b/src/strcasestr.c
index 2077dc3ff..86c7ec5b0 100644
--- a/src/strcasestr.c
+++ b/src/strcasestr.c
@@ -75,7 +75,7 @@ strcasestr (const char *s, const char *q)
 	if (!( (intptr_t)up|(intptr_t)lp ))
 		return 0;
 
-	if (!lp || up < lp)
+	if (!lp || ( up && up < lp ))
 	{
 		ppa = &up;
 		ppb = &lp;