diff --git a/.github/workflows/build_and_test.yml b/.github/workflows/build_and_test.yml
index c0c63ea..1212169 100644
--- a/.github/workflows/build_and_test.yml
+++ b/.github/workflows/build_and_test.yml
@@ -10,6 +10,9 @@ on:
   pull_request:
     branches:
 
+# Declare default permissions as read only.
+permissions: read-all
+
 jobs:
 
   build-and-test: