diff --git a/src/main/scala/sbtghactions/GenerativePlugin.scala b/src/main/scala/sbtghactions/GenerativePlugin.scala
index 20ec9a2..025335a 100644
--- a/src/main/scala/sbtghactions/GenerativePlugin.scala
+++ b/src/main/scala/sbtghactions/GenerativePlugin.scala
@@ -292,7 +292,7 @@ ${indent(rendered.mkString("\n"), 1)}"""
     val runsOn = if (job.runsOnExtraLabels.isEmpty)
       s"$${{ matrix.os }}"
     else
-      job.runsOnExtraLabels.mkString(s"[ $${{ matrix.os }}, ", ", ", " ]" )
+      job.runsOnExtraLabels.mkString(s"""[ "$${{ matrix.os }}", """, ", ", " ]" )
 
     val body = s"""name: ${wrap(job.name)}${renderedNeeds}${renderedCond}
 strategy:
diff --git a/src/test/scala/sbtghactions/GenerativePluginSpec.scala b/src/test/scala/sbtghactions/GenerativePluginSpec.scala
index 1bd1b22..ccd924d 100644
--- a/src/test/scala/sbtghactions/GenerativePluginSpec.scala
+++ b/src/test/scala/sbtghactions/GenerativePluginSpec.scala
@@ -405,7 +405,7 @@ class GenerativePluginSpec extends Specification {
       os: [ubuntu-latest]
       scala: [2.13.1]
       java: [adopt@1.8]
-  runs-on: [ ${{ matrix.os }}, runner-label, runner-group ]
+  runs-on: [ "${{ matrix.os }}", runner-label, runner-group ]
   steps:
     - run: echo hello"""
     }