diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index e30f55e0c9..1ae3698cb1 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -25,7 +25,7 @@ jobs:
       PETSC_ARCH: ""
       SLEPC_DIR: /usr/lib/slepcdir/slepc3.12/x86_64-linux-gnu-real/
       SLEPC_ARCH: ""
-      OMP_NUM_THREADS: ${{ matrix.config.omp_num_threads }}
+      OMP_NUM_THREADS: ${{ matrix.config.omp_num_threads || 1 }}
       PYTHONPATH: ${{ github.workspace }}/tools/pylib
       OMPI_MCA_rmaps_base_oversubscribe: yes
       PRTE_MCA_rmaps_default_mapping_policy: ":oversubscribe"