diff --git a/ConflictSet.cpp b/ConflictSet.cpp
index 0148a6e..fa98f1c 100644
--- a/ConflictSet.cpp
+++ b/ConflictSet.cpp
@@ -741,6 +741,7 @@ bytes:
 
 int longestCommonPrefixPartialKey(const uint8_t *ap, const uint8_t *bp,
                                   int cl) {
+  assert(cl <= Node::kPartialKeyMaxLen);
   int i = 0;
   for (; i < cl; ++i) {
     if (*ap++ != *bp++) {