diff --git a/.github/workflows/test_with_deepl_mock.yml b/.github/workflows/test_with_deepl_mock.yml
index 9aa0369..01c474e 100644
--- a/.github/workflows/test_with_deepl_mock.yml
+++ b/.github/workflows/test_with_deepl_mock.yml
@@ -58,7 +58,7 @@ jobs:
         run: shards install --without-development
 
       - name: Run tests
-        run: crystal spec
+        run: crystal spec -Ddeepl_mock
         env:
           DEEPL_SERVER_URL: http://localhost:3000
           HTTP_PROXY: http://localhost:3001
diff --git a/spec/spec_helper.cr b/spec/spec_helper.cr
index 59c2621..f86d98b 100644
--- a/spec/spec_helper.cr
+++ b/spec/spec_helper.cr
@@ -1,3 +1,6 @@
 require "spec"
+{% if flag?(:deepl_mock) %}
+STDERR.puts " Using mock for DeepL API ".colorize.back(:magenta)
 require "./crest_extension_for_mock"
+{% end %}
 require "../src/deepl"