diff --git a/libcxx/utils/ci/run-buildbot b/libcxx/utils/ci/run-buildbot
--- a/libcxx/utils/ci/run-buildbot
+++ b/libcxx/utils/ci/run-buildbot
@@ -12,6 +12,8 @@
 unset LANG
 unset LC_ALL
 unset LC_COLLATE
+export CC=clang-15
+export CXX=clang++-15
 
 PROGNAME="$(basename "${0}")"
 
@@ -370,6 +372,8 @@
     check-runtimes
 ;;
 apple-system)
+    export -n CC
+    export -n CXX
     clean
 
     arch="$(uname -m)"
@@ -386,6 +390,8 @@
     xcrun --sdk macosx ninja -vC "${BUILD_DIR}/${arch}" check-cxx check-cxxabi check-cxx-abilist
 ;;
 apple-system-backdeployment-*)
+    export -n CC
+    export -n CXX
     clean
 
     if [[ "${OSX_ROOTS}" == "" ]]; then
@@ -484,11 +490,15 @@
     check-runtimes
 ;;
 aarch64)
+    export -n CC
+    export -n CXX
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/AArch64.cmake"
     check-runtimes
 ;;
 aarch64-noexceptions)
+    export -n CC
+    export -n CXX
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/AArch64.cmake" \
                    -DLIBCXX_ENABLE_EXCEPTIONS=OFF \
@@ -497,6 +507,8 @@
 ;;
 # Aka Armv8 32 bit
 armv8)
+    export -n CC
+    export -n CXX
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Armv8Arm.cmake"
     check-runtimes
@@ -508,11 +520,15 @@
 ;;
 # Armv7 32 bit. One building Arm only one Thumb only code.
 armv7)
+    export -n CC
+    export -n CXX
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Armv7Arm.cmake"
     check-runtimes
 ;;
 armv7-noexceptions)
+    export -n CC
+    export -n CXX
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Armv7Thumb-noexceptions.cmake"
     check-runtimes