diff --git a/.github/workflows/test-build.yml b/.github/workflows/test-build.yml
index 95af300c9..6a69caaea 100644
--- a/.github/workflows/test-build.yml
+++ b/.github/workflows/test-build.yml
@@ -56,6 +56,7 @@ jobs:
           mkdir build
           cd build
           make -f ../Makefile config-$CC
+          echo 'SANITIZER = undefined' >> Makefile.conf
           make -f ../Makefile -j$procs ENABLE_LTO=1
 
       - name: Log yosys-config output
@@ -82,6 +83,7 @@ jobs:
     if: needs.pre_job.outputs.should_skip != 'true'
     env:
       CC: clang
+      UBSAN_OPTIONS: halt_on_error=1
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest]