diff --git a/.github/workflows/build-images.yml b/.github/workflows/build-images.yml
index 2aa9e1d..a443c79 100644
--- a/.github/workflows/build-images.yml
+++ b/.github/workflows/build-images.yml
@@ -10,7 +10,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@ee0669bd1cc54295c223e0bb666b733df41de1c5 # v2
 
     - name: Log in to Docker Hub
       if: github.ref == 'refs/heads/master'
diff --git a/Dockerfile b/Dockerfile
index 9abbc93..d5c89b6 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -6,7 +6,7 @@ LABEL maintainer="Rezoleo <contact@rezoleo.fr>"
 
 # We will use the php installer from mlocati
 # https://github.com/mlocati/docker-php-extension-installer
-COPY --from=mlocati/php-extension-installer /usr/bin/install-php-extensions /usr/local/bin/
+COPY --from=mlocati/php-extension-installer@sha256:517b3f8a0221182fbcf884fdefc7c66a4099e7935311365d47b6d737acc4270f /usr/bin/install-php-extensions /usr/local/bin/
 
 RUN apt-get update \
      # Let's update the base layer for security fixes, see