diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d57edf54..a2842187 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -69,7 +69,7 @@ jobs:
             export LUISA_CC=gcc-${{ matrix.compiler.version }}
             export LUISA_CXX=g++-${{ matrix.compiler.version }}
             export LUISA_FLAGS=""
-            if [ "${{ config }}" = "Debug" ]; then
+            if [ "${{ matrix.config }}" = "Debug" ]; then
               export CMAKE_BUILD_PARALLEL_LEVEL=1 # to avoid OOM on GitHub Actions
             fi
           else