diff --git a/.github/actions/test_firedrake/action.yml b/.github/actions/test_firedrake/action.yml
index 388045dae4..8794fbc58d 100644
--- a/.github/actions/test_firedrake/action.yml
+++ b/.github/actions/test_firedrake/action.yml
@@ -2,6 +2,8 @@ name: Run Firedrake tests
 description: Run Firedrake test suite for a given amount of parallelism.
 inputs:
   nprocs:
+    description: Number of processes
+    required: true
 
 runs:
   using: "composite"