diff --git a/src/flb_pack.c b/src/flb_pack.c
index 2dc3d1e38e7..446bc05c96f 100644
--- a/src/flb_pack.c
+++ b/src/flb_pack.c
@@ -1478,9 +1478,10 @@ char *flb_msgpack_to_json_str(size_t size, const msgpack_object *obj, int escape
 
     while (1) {
         ret = flb_msgpack_to_json(buf, size, obj, escape_unicode);
-        if (ret <= 0) {
+        if (ret < 0) {
             /* buffer is small. retry.*/
             size *= 2;
+            flb_info("failed to convert msgpack to json, retrying with new size=%zu", size);
             tmp = flb_realloc(buf, size);
             if (tmp) {
                 buf = tmp;
@@ -1491,6 +1492,12 @@ char *flb_msgpack_to_json_str(size_t size, const msgpack_object *obj, int escape
                 return NULL;
             }
         }
+        else if (ret == 0) {
+            /* nothing to pack */
+            flb_warn("unexpected result from flb_msgpack_to_json: 0");
+            flb_free(buf);
+            return NULL;
+        }
         else {
             break;
         }