diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index af19602..797c22e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -16,14 +16,14 @@ jobs:
         jdk: [8, 9, 11, 15]
     runs-on: ${{ matrix.os }}
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@ee0669bd1cc54295c223e0bb666b733df41de1c5 # v2.7.0
       - name: Set up JDK
-        uses: actions/setup-java@v2
+        uses: actions/setup-java@91d3aa4956ec4a53e477c4907347b5e3481be8c9 # v2.5.1
         with:
           java-version: ${{ matrix.jdk }}
           distribution: zulu
       - name: Cache Maven packages
-        uses: actions/cache@v2
+        uses: actions/cache@2b250bc32ad02700b996b496c14ac8c2840a2991 # v2.1.8
         with:
           path: ~/.m2
           key: ${{ runner.os }}-m2-${{ hashFiles('**/pom.xml') }}