diff --git a/src/networking.c b/src/networking.c
index 31c6664c7..e267565a6 100644
--- a/src/networking.c
+++ b/src/networking.c
@@ -492,6 +492,7 @@ void *addReplyDeferredLen(client *c) {
 
 /* Populate the length object and try gluing it to the next chunk. */
 void setDeferredAggregateLen(client *c, void *node, long length, char prefix) {
+    serverAssert(length >= 0);
     listNode *ln = (listNode*)node;
     clientReplyBlock *next;
     char lenstr[128];