diff --git a/utils/bazel/llvm-project-overlay/llvm/include/llvm/Config/llvm-config.h b/utils/bazel/llvm-project-overlay/llvm/include/llvm/Config/llvm-config.h
index 5aeceb4ac1cc..6cd89102a28e 100644
--- a/utils/bazel/llvm-project-overlay/llvm/include/llvm/Config/llvm-config.h
+++ b/utils/bazel/llvm-project-overlay/llvm/include/llvm/Config/llvm-config.h
@@ -117,4 +117,11 @@
 /* Define if building LLVM with BUILD_SHARED_LIBS */
 /* #undef LLVM_BUILD_SHARED_LIBS */
 
+/* Define if building LLVM with LLVM_FORCE_USE_OLD_TOOLCHAIN_LIBS */
+#cmakedefine LLVM_FORCE_USE_OLD_TOOLCHAIN ${LLVM_FORCE_USE_OLD_TOOLCHAIN}
+
+/* Define if llvm_unreachable should be optimized with undefined behavior
+ * in non assert builds */
+/* #undef LLVM_UNREACHABLE_OPTIMIZE */
+
 #endif
diff --git a/utils/bazel/llvm_configs/llvm-config.h.cmake b/utils/bazel/llvm_configs/llvm-config.h.cmake
index d8edf33ba0ce..f8281d829792 100644
--- a/utils/bazel/llvm_configs/llvm-config.h.cmake
+++ b/utils/bazel/llvm_configs/llvm-config.h.cmake
@@ -112,4 +112,8 @@
 /* Define if building LLVM with LLVM_FORCE_USE_OLD_TOOLCHAIN_LIBS */
 #cmakedefine LLVM_FORCE_USE_OLD_TOOLCHAIN ${LLVM_FORCE_USE_OLD_TOOLCHAIN}
 
+/* Define if llvm_unreachable should be optimized with undefined behavior
+ * in non assert builds */
+#cmakedefine01 LLVM_UNREACHABLE_OPTIMIZE
+
 #endif