diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index f22553b..82baa5a 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -33,6 +33,7 @@ jobs:
           cache-write: ${{ github.event_name == 'push' && github.ref_name == 'main' }}
           environments: test-cpu
           activate-environment: true
+          frozen: true
       - name: Run pytest
         shell: bash {0}
         run: pixi run -e test-cpu tests
@@ -52,6 +53,7 @@ jobs:
           cache: true
           cache-write: ${{ github.event_name == 'push' && github.ref_name == 'main' }}
           environments: mypy
+          frozen: true
       - name: Run mypy
         shell: bash {0}
         run: pixi run mypy
@@ -66,6 +68,7 @@ jobs:
           cache: true
           cache-write: ${{ github.event_name == 'push' && github.ref_name == 'main' }}
           environments: test-cpu
+          frozen: true
       - name: Run explanation notebooks
         shell: bash {0}
         run: pixi run -e test-cpu explanation-notebooks