diff --git a/src/bee_tree.c b/src/bee_tree.c
index a0f297f..c3cc0b4 100644
--- a/src/bee_tree.c
+++ b/src/bee_tree.c
@@ -327,7 +327,7 @@ static struct bee_subtree *bee_tree_insert_node(struct bee_tree *tree, struct be
                 return NULL;
         }
 
-        if (tree->flags & (BEE_TREE_FLAG_UNIQUE_DATA|BEE_TREE_FLAG_COMPARE_DATA_ON_EQUAL_KEY)) {
+        if ((cmp == 0) && tree->flags & (BEE_TREE_FLAG_UNIQUE_DATA|BEE_TREE_FLAG_COMPARE_DATA_ON_EQUAL_KEY)) {
 
             assert(tree->compare_data);