diff --git a/test/e2e-common.sh b/test/e2e-common.sh
index 6c443c0d9..b6f783003 100755
--- a/test/e2e-common.sh
+++ b/test/e2e-common.sh
@@ -163,6 +163,8 @@ function gateway_conformance() {
 }
 
 function test_e2e() {
+  # TestGatewayWithNoService edits the ConfigMap, so running in parallel could cause
+  # unexpected problems when more tests are added.
   local parallel_count="1"