diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index fa394d6a..c7a665a8 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -76,7 +76,7 @@ rubocop:
   - *apk-add
   - *disable-hainish
   script:
-  - "./bin/modified_files | grep .rb | xargs -r go-task bundle -- exec rubocop"
+  - "./bin/modified_files | ./bin/with_extension rb | xargs -r go-task bundle -- exec rubocop"
 haml:
   stage: "test"
   cache:
@@ -87,4 +87,4 @@ haml:
   - *apk-add
   - *disable-hainish
   script:
-  - "./bin/modified_files | grep .haml | xargs -r go-task bundle -- exec haml-lint"
+  - "./bin/modified_files | ./bin/with_extension haml | xargs -r go-task bundle -- exec haml-lint"
diff --git a/bin/with_extension b/bin/with_extension
new file mode 100755
index 00000000..129122dc
--- /dev/null
+++ b/bin/with_extension
@@ -0,0 +1,4 @@
+#!/bin/sh
+
+grep "\.${1}$"
+exit 0