diff --git a/.github/workflows/build-crystal-containers.yml b/.github/workflows/build-crystal-containers.yml
index 09edf13..bbef40e 100644
--- a/.github/workflows/build-crystal-containers.yml
+++ b/.github/workflows/build-crystal-containers.yml
@@ -20,21 +20,21 @@ jobs:
           # stable release version
           - version: 1.14.0
             shards: 0.18.0
-            alpine: 3.20
+            alpine: '3.20'
             libgc: 8.2.6
             llvm: 18
             tag: latest
           # release candidate, builds should target compatibility
           - version: 1.14.0
             shards: 0.18.0
-            alpine: 3.20
+            alpine: '3.20'
             libgc: 8.2.6
             llvm: 18
             tag: unstable
           # latest version with unknown side effects
           - version: 1.14.0
             shards: 0.18.0
-            alpine: 3.20
+            alpine: '3.20'
             libgc: 8.2.6
             llvm: 18
             tag: experimental