diff --git a/.github/workflows/backend.yaml b/.github/workflows/backend.yaml
index 263cef763e..2e35ba4bc3 100644
--- a/.github/workflows/backend.yaml
+++ b/.github/workflows/backend.yaml
@@ -89,7 +89,7 @@ jobs:
       fail-fast: true
       matrix:
         jdk: [8, 11]
-        flink: [1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20]
+        flink: ['1.14', '1.15', '1.16', '1.17', '1.18', '1.19', '1.20']
 
     timeout-minutes: 30
     env: