diff --git a/whisper/whisper_test.go b/whisper/whisper_test.go
index b5a919984..1a9a8667a 100644
--- a/whisper/whisper_test.go
+++ b/whisper/whisper_test.go
@@ -189,13 +189,22 @@ func TestMessageExpiration(t *testing.T) {
 		t.Fatalf("failed to inject message: %v", err)
 	}
 	// Check that the message is inside the cache
-	if _, ok := node.messages[envelope.Hash()]; !ok {
+	node.poolMu.RLock()
+	_, found := node.messages[envelope.Hash()]
+	node.poolMu.RUnlock()
+
+	if !found {
 		t.Fatalf("message not found in cache")
 	}
 	// Wait for expiration and check cache again
 	time.Sleep(time.Second)     // wait for expiration
 	time.Sleep(expirationCycle) // wait for cleanup cycle
-	if _, ok := node.messages[envelope.Hash()]; ok {
+
+	node.poolMu.RLock()
+	_, found = node.messages[envelope.Hash()]
+	node.poolMu.RUnlock()
+
+	if found {
 		t.Fatalf("message not expired from cache")
 	}
 }