diff --git a/src/common/container.c b/src/common/container.c
index ffb4ffe497..8021bd19c3 100644
--- a/src/common/container.c
+++ b/src/common/container.c
@@ -358,6 +358,8 @@ smartlist_split_string(smartlist_t *sl, const char *str, const char *sep,
         ;
     }
 
+    tor_assert(end);
+
     if (!*end) {
       next = NULL;
     } else if (sep) {