diff --git a/.github/workflows/cmake.yml b/.github/workflows/cmake.yml
index 75688625eb..1acc320e11 100644
--- a/.github/workflows/cmake.yml
+++ b/.github/workflows/cmake.yml
@@ -204,6 +204,7 @@ jobs:
             -DCMAKE_C_COMPILER=gcc-12 \
             -DCMAKE_CXX_COMPILER=g++-12 \
             -DENABLE_UNDEFINED_SANITIZER=ON \
+            -DUNDEFINED_BEHAVIOR_IS_FATAL=ON \
             -DDUMP_REGIONS_ON_CRASH=ON \
             -DENABLE_PCI_IDS_DOWNLOAD=OFF \
             -DENABLE_USB_IDS_DOWNLOAD=OFF
diff --git a/Meta/Azure/Serenity.yml b/Meta/Azure/Serenity.yml
index 844a07bf67..a4c62f1b1c 100644
--- a/Meta/Azure/Serenity.yml
+++ b/Meta/Azure/Serenity.yml
@@ -47,6 +47,7 @@ jobs:
           -DSERENITY_ARCH=${{ parameters.arch }} \
           -DSERENITY_TOOLCHAIN=Clang \
           -DENABLE_UNDEFINED_SANITIZER=ON \
+          -DUNDEFINED_BEHAVIOR_IS_FATAL=ON \
           -DENABLE_USERSPACE_COVERAGE_COLLECTION=${{ parameters.coverage }} \
           -DDUMP_REGIONS_ON_CRASH=ON \
           -DENABLE_PCI_IDS_DOWNLOAD=OFF \