diff --git a/.github/workflows/ubuntu-matrix.yml b/.github/workflows/ubuntu-matrix.yml
index 95083041..c93b095f 100644
--- a/.github/workflows/ubuntu-matrix.yml
+++ b/.github/workflows/ubuntu-matrix.yml
@@ -165,7 +165,7 @@ jobs:
         config:
         - { name: shared, amflags: STATIC=0 }
         - { name: static, amflags: STATIC=1 }
-        os: buster
+        os: [ buster ]
         exclude:
           - platform: { targetos: linux-arm }
             config: { name: shared }