diff --git a/lib/support/flattenMessage.js b/lib/support/flattenMessage.js
index cf142ba6b..ba4d526d9 100644
--- a/lib/support/flattenMessage.js
+++ b/lib/support/flattenMessage.js
@@ -72,7 +72,7 @@ module.exports = {
         }
           break;
         default:
-          throw new Error('Unhandled value type ' + valueType + ' found when flattening data');
+          throw new Error('Unhandled value type ' + valueType + ' found when flattening data for prefix ' + keyPrefix);
       }
     }