diff --git a/src/modules/flow/json/json.c b/src/modules/flow/json/json.c
index 51d32a9a6..4d82ecb72 100644
--- a/src/modules/flow/json/json.c
+++ b/src/modules/flow/json/json.c
@@ -973,8 +973,10 @@ json_serialize(struct sol_buffer *buffer, struct json_element *element)
         SOL_INT_CHECK(r, < 0, r);
 
         SOL_VECTOR_FOREACH_IDX (&element->children, key_element, i) {
-            if (i > 0)
+            if (i > 0) {
                 r = sol_buffer_append_char(buffer, ',');
+                SOL_INT_CHECK(r, < 0, r);
+            }
             r = json_serialize_key_element(buffer, key_element);
             SOL_INT_CHECK(r, < 0, r);
         }