diff --git a/.github/workflows/image_app.yml b/.github/workflows/image_app.yml
index f7f16b11..d32ea5b5 100644
--- a/.github/workflows/image_app.yml
+++ b/.github/workflows/image_app.yml
@@ -24,7 +24,7 @@ on:
         description: "The platforms to build for."
 
 env:
-  FLAVOR_PREFIX: ${{ inputs.flavor && inputs.flavor + '-' || '' }}
+  FLAVOR_PREFIX: ${{ inputs.flavor && format('{0}-', inputs.flavor) || '' }}
 
 jobs:
   build-app: