diff --git a/src/cls/rbd/cls_rbd.cc b/src/cls/rbd/cls_rbd.cc
index 2ab186bf6aa..43c717de3fd 100644
--- a/src/cls/rbd/cls_rbd.cc
+++ b/src/cls/rbd/cls_rbd.cc
@@ -2630,7 +2630,7 @@ static const string metadata_name_from_key(const string &key)
  * Input:
  * @param start_after which name to begin listing after
  *        (use the empty string to start at the beginning)
- * @param max_return the maximum number of names to list(if 0 means no limit)
+ * @param max_return the maximum number of names to list
 
  * Output:
  * @param value
@@ -2649,33 +2649,33 @@ int metadata_list(cls_method_context_t hctx, bufferlist *in, bufferlist *out)
     return -EINVAL;
   }
 
+  // TODO remove implicit support for zero during the N-release
+  if (max_return == 0) {
+    max_return = RBD_MAX_KEYS_READ;
+  }
+
   map<string, bufferlist> data;
   string last_read = metadata_key_for_name(start_after);
-  int max_read = max_return ? MIN(RBD_MAX_KEYS_READ, max_return) : RBD_MAX_KEYS_READ;
-  bool more;
+  bool more = true;
 
-  do {
+  while (more && data.size() < max_return) {
     map<string, bufferlist> raw_data;
+    int max_read = MIN(RBD_MAX_KEYS_READ, max_return - data.size());
     int r = cls_cxx_map_get_vals(hctx, last_read, RBD_METADATA_KEY_PREFIX,
                                  max_read, &raw_data, &more);
     if (r < 0) {
       CLS_ERR("failed to read the vals off of disk: %s", cpp_strerror(r).c_str());
       return r;
     }
-    if (raw_data.empty())
-      break;
 
-    map<string, bufferlist>::iterator it = raw_data.begin();
-    for (; it != raw_data.end(); ++it)
-      data[metadata_name_from_key(it->first)].swap(it->second);
+    for (auto& kv : raw_data) {
+      data[metadata_name_from_key(kv.first)].swap(kv.second);
+    }
 
-    if (!more)
-      break;
-
-    last_read = raw_data.rbegin()->first;
-    if (max_return)
-      max_read = MIN(RBD_MAX_KEYS_READ, max_return - data.size());
-  } while (more);
+    if (!raw_data.empty()) {
+      last_read = raw_data.rbegin()->first;
+    }
+  }
 
   ::encode(data, *out);
   return 0;