diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 2f91df8..dd78b0e 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -26,6 +26,7 @@ jobs:
     env:
       PMG_MAPI_KEY: ${{ secrets.PMG_MAPI_KEY }}
       PMG_VASP_PSP_DIR: "${{ github.workspace }}/psp"
+      MPLBACKEND: Agg  # non-interactive backend for matplotlib
 
     steps:
       - name: Check out repo