diff --git a/server/core/config_runtime.cc b/server/core/config_runtime.cc
index d4af11044..d87773abb 100644
--- a/server/core/config_runtime.cc
+++ b/server/core/config_runtime.cc
@@ -3020,6 +3020,7 @@ bool runtime_alter_maxscale_from_json(json_t* new_json)
                 rval = false;
             }
         }
+        json_decref(old_json);
     }
 
     return rval;