diff --git a/.github/workflows/ubuntu.yml b/.github/workflows/ubuntu.yml
index 2b4ac751bc907a..d2a736991b2636 100644
--- a/.github/workflows/ubuntu.yml
+++ b/.github/workflows/ubuntu.yml
@@ -115,7 +115,7 @@ jobs:
         run: >
           mkdir ${{ matrix.shared_gc_dir }} &&
           LD_LIBRARY_PATH=/home/runner/work/ruby/ruby/src/gc/mmtk/target/release
-          make shared-gc SHARED_GC=${{ matrix.gc_name }} MMTK_BUILD=debug
+          make shared-gc SHARED_GC=${{ matrix.gc_name }} MMTK_BUILD=release
         if: ${{ matrix.shared_gc }}
 
       - run: $SETARCH make