diff --git a/libcxx/test/configs/llvm-libc++-shared-clangcl.cfg.in b/libcxx/test/configs/llvm-libc++-shared-clangcl.cfg.in
--- a/libcxx/test/configs/llvm-libc++-shared-clangcl.cfg.in
+++ b/libcxx/test/configs/llvm-libc++-shared-clangcl.cfg.in
@@ -3,12 +3,19 @@
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
+dbg_include = ''
+lib_suffix = ''
+
+if '@uppercase_CMAKE_BUILD_TYPE@' == 'DEBUG':
+    dbg_include = ' -D_DEBUG -include set_windows_crt_report_mode.h'
+    lib_suffix = 'd'
+
 config.substitutions.append(('%{flags}', '--driver-mode=g++'))
 config.substitutions.append(('%{compile_flags}',
-    '-nostdinc++ -I %{include} -I %{target-include} -I %{libcxx}/test/support -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_STDIO_ISO_WIDE_SPECIFIERS -DNOMINMAX'
+    '-nostdinc++ -I %{include} -I %{target-include} -I %{libcxx}/test/support -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_STDIO_ISO_WIDE_SPECIFIERS -DNOMINMAX' + dbg_include
 ))
 config.substitutions.append(('%{link_flags}',
-    '-nostdlib -L %{lib} -lc++ -lmsvcrt -lmsvcprt -loldnames'
+    '-nostdlib -L %%{lib} -lc++ -lmsvcrt%s -lmsvcprt%s -loldnames' % (lib_suffix, lib_suffix)
 ))
 config.substitutions.append(('%{exec}',
     '%{executor} --execdir %T --prepend_env PATH=%{lib} -- '
diff --git a/libcxx/test/configs/llvm-libc++-shared-no-vcruntime-clangcl.cfg.in b/libcxx/test/configs/llvm-libc++-shared-no-vcruntime-clangcl.cfg.in
--- a/libcxx/test/configs/llvm-libc++-shared-no-vcruntime-clangcl.cfg.in
+++ b/libcxx/test/configs/llvm-libc++-shared-no-vcruntime-clangcl.cfg.in
@@ -4,12 +4,19 @@
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
+dbg_include = ''
+lib_suffix = ''
+
+if '@uppercase_CMAKE_BUILD_TYPE@' == 'DEBUG':
+    dbg_include = ' -D_DEBUG -include set_windows_crt_report_mode.h'
+    lib_suffix = 'd'
+
 config.substitutions.append(('%{flags}', '--driver-mode=g++'))
 config.substitutions.append(('%{compile_flags}',
-    '-nostdinc++ -I %{include} -I %{target-include} -I %{libcxx}/test/support -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_STDIO_ISO_WIDE_SPECIFIERS -DNOMINMAX -D_HAS_EXCEPTIONS=0'
+    '-nostdinc++ -I %{include} -I %{target-include} -I %{libcxx}/test/support -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_STDIO_ISO_WIDE_SPECIFIERS -DNOMINMAX -D_HAS_EXCEPTIONS=0' + dbg_include
 ))
 config.substitutions.append(('%{link_flags}',
-    '-nostdlib -L %{lib} -lc++ -lmsvcrt -lmsvcprt -loldnames'
+    '-nostdlib -L %%{lib} -lc++ -lmsvcrt%s -lmsvcprt%s -loldnames' % (lib_suffix, lib_suffix)
 ))
 config.substitutions.append(('%{exec}',
     '%{executor} --execdir %T --prepend_env PATH=%{lib} -- '
diff --git a/libcxx/test/configs/llvm-libc++-static-clangcl.cfg.in b/libcxx/test/configs/llvm-libc++-static-clangcl.cfg.in
--- a/libcxx/test/configs/llvm-libc++-static-clangcl.cfg.in
+++ b/libcxx/test/configs/llvm-libc++-static-clangcl.cfg.in
@@ -3,12 +3,19 @@
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
+dbg_include = ''
+lib_suffix = ''
+
+if '@uppercase_CMAKE_BUILD_TYPE@' == 'DEBUG':
+    dbg_include = ' -D_DEBUG -include set_windows_crt_report_mode.h'
+    lib_suffix = 'd'
+
 config.substitutions.append(('%{flags}', '--driver-mode=g++'))
 config.substitutions.append(('%{compile_flags}',
-    '-nostdinc++ -I %{include} -I %{target-include} -I %{libcxx}/test/support -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_STDIO_ISO_WIDE_SPECIFIERS -DNOMINMAX'
+    '-nostdinc++ -I %{include} -I %{target-include} -I %{libcxx}/test/support -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_STDIO_ISO_WIDE_SPECIFIERS -DNOMINMAX' + dbg_include
 ))
 config.substitutions.append(('%{link_flags}',
-    '-nostdlib -L %{lib} -llibc++ -lmsvcrt -lmsvcprt -loldnames'
+    '-nostdlib -L %%{lib} -llibc++ -lmsvcrt%s -lmsvcprt%s -loldnames' % (lib_suffix, lib_suffix)
 ))
 config.substitutions.append(('%{exec}',
     '%{executor} --execdir %T -- '
diff --git a/libcxx/test/support/set_windows_crt_report_mode.h b/libcxx/test/support/set_windows_crt_report_mode.h
--- a/libcxx/test/support/set_windows_crt_report_mode.h
+++ b/libcxx/test/support/set_windows_crt_report_mode.h
@@ -10,6 +10,14 @@
 #ifndef SUPPORT_SET_WINDOWS_CRT_REPORT_MODE_H
 #define SUPPORT_SET_WINDOWS_CRT_REPORT_MODE_H
 
+// A few tests are built in C mode or in C++03 mode. The initialization
+// of init_crt_anchor is a C++ feature, and <crtdbg.h> ends up including
+// MSVC header code which breaks in C++03 mode. Therefore, only expand
+// the body of this header when included in C++ >= 11 mode. As this file
+// is included in every single translation unit, we're intentionally not
+// including test_macros.h (for TEST_STD_VER) but try to keep it to the
+// bare minimum.
+#if defined(__cplusplus) && __cplusplus > 199711L
 #ifndef _DEBUG
 #error _DEBUG must be defined when using this header
 #endif
@@ -32,5 +40,6 @@
 }
 
 static int init_crt_anchor = init_crt_report_mode();
+#endif // defined(__cplusplus) && __cplusplus > 199711L
 
 #endif // SUPPORT_SET_WINDOWS_CRT_REPORT_MODE_H
diff --git a/libcxx/utils/ci/buildkite-pipeline.yml b/libcxx/utils/ci/buildkite-pipeline.yml
--- a/libcxx/utils/ci/buildkite-pipeline.yml
+++ b/libcxx/utils/ci/buildkite-pipeline.yml
@@ -764,6 +764,19 @@
           - exit_status: -1  # Agent was lost
             limit: 2
 
+    - label: "Clang-cl (Debug mode)"
+      command: "bash libcxx/utils/ci/run-buildbot clang-cl-debug"
+      artifact_paths:
+        - "**/test-results.xml"
+        - "**/*.abilist"
+      agents:
+        queue: "windows"
+      retry:
+        automatic:
+          - exit_status: -1  # Agent was lost
+            limit: 2
+      timeout_in_minutes: 120
+
     - label: "MinGW (DLL, x86_64)"
       command: "bash libcxx/utils/ci/run-buildbot mingw-dll"
       artifact_paths:
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
@@ -639,6 +639,13 @@
     echo "+++ Running the libc++ tests"
     ${NINJA} -vC "${BUILD_DIR}" check-cxx
 ;;
+clang-cl-debug)
+    clean
+    generate-cmake-libcxx-win -DLIBCXX_TEST_PARAMS="enable_experimental=False" \
+                              -DCMAKE_BUILD_TYPE=Debug
+    echo "+++ Running the libc++ tests"
+    ${NINJA} -vC "${BUILD_DIR}" check-cxx
+;;
 mingw-dll)
     clean
     # Explicitly specify the compiler with a triple prefix. The CI