diff --git a/src/instrumentation/index.js b/src/instrumentation/index.js
index <HASH>..<HASH> 100644
--- a/src/instrumentation/index.js
+++ b/src/instrumentation/index.js
@@ -84,7 +84,7 @@ function getRawGroupedTracesTimings (traces, groupedTraces) {
   }
 
   var groupedByTransaction = grouper(traces, function (trace) {
-    return trace.transaction.name
+    return trace.transaction.name + '|' + trace.transaction._start
   })
 
   return Object.keys(groupedByTransaction).map(function (key) {
Use transaction name + transaction start as grouping keys

Transactions can have same name, so include start time to make sure transactions and traces are grouped correctly.