diff --git a/libcxx/cmake/caches/Armv7Arm.cmake b/libcxx/cmake/caches/Armv7Arm.cmake
index e60d43f33dde7..be8f9ff74a8e4 100644
--- a/libcxx/cmake/caches/Armv7Arm.cmake
+++ b/libcxx/cmake/caches/Armv7Arm.cmake
@@ -1,3 +1,5 @@
 set(CMAKE_CXX_COMPILER_TARGET "armv7l-linux-gnueabihf" CACHE STRING "")
 set(CMAKE_CXX_FLAGS "-marm" CACHE STRING "")
 set(CMAKE_C_FLAGS "-marm" CACHE STRING "")
+set(LIBCXX_TEST_PARAMS "enable_modules=clang" CACHE STRING "")
+set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
diff --git a/libcxx/cmake/caches/Armv7Thumb-no-exceptions.cmake b/libcxx/cmake/caches/Armv7Thumb-no-exceptions.cmake
index 70b619f8ec31f..5ddfa15d77a49 100644
--- a/libcxx/cmake/caches/Armv7Thumb-no-exceptions.cmake
+++ b/libcxx/cmake/caches/Armv7Thumb-no-exceptions.cmake
@@ -3,3 +3,5 @@ set(CMAKE_CXX_FLAGS "-mthumb" CACHE STRING "")
 set(CMAKE_C_FLAGS "-mthumb" CACHE STRING "")
 set(LIBCXX_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
 set(LIBCXXABI_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
+set(LIBCXX_TEST_PARAMS "enable_modules=clang" CACHE STRING "")
+set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
diff --git a/libcxx/cmake/caches/Armv8Arm.cmake b/libcxx/cmake/caches/Armv8Arm.cmake
index a289471603530..e0379b5870bdf 100644
--- a/libcxx/cmake/caches/Armv8Arm.cmake
+++ b/libcxx/cmake/caches/Armv8Arm.cmake
@@ -1,3 +1,5 @@
 set(CMAKE_CXX_COMPILER_TARGET "armv8l-linux-gnueabihf" CACHE STRING "")
 set(CMAKE_CXX_FLAGS "-marm" CACHE STRING "")
 set(CMAKE_C_FLAGS "-marm" CACHE STRING "")
+set(LIBCXX_TEST_PARAMS "enable_modules=clang" CACHE STRING "")
+set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
diff --git a/libcxx/cmake/caches/Armv8Thumb-no-exceptions.cmake b/libcxx/cmake/caches/Armv8Thumb-no-exceptions.cmake
index b4c7dfca279cd..b0a53484961e4 100644
--- a/libcxx/cmake/caches/Armv8Thumb-no-exceptions.cmake
+++ b/libcxx/cmake/caches/Armv8Thumb-no-exceptions.cmake
@@ -3,3 +3,5 @@ set(CMAKE_CXX_FLAGS "-mthumb" CACHE STRING "")
 set(CMAKE_C_FLAGS "-mthumb" CACHE STRING "")
 set(LIBCXX_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
 set(LIBCXXABI_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
+set(LIBCXX_TEST_PARAMS "enable_modules=clang" CACHE STRING "")
+set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
diff --git a/libcxx/cmake/caches/Generic-hardening-mode-debug.cmake b/libcxx/cmake/caches/Generic-hardening-mode-debug.cmake
index 1d401ba69ab80..483e8a71da73d 100644
--- a/libcxx/cmake/caches/Generic-hardening-mode-debug.cmake
+++ b/libcxx/cmake/caches/Generic-hardening-mode-debug.cmake
@@ -1 +1,3 @@
 set(LIBCXX_HARDENING_MODE "debug" CACHE STRING "")
+set(LIBCXX_TEST_PARAMS "enable_modules=clang" CACHE STRING "")
+set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
diff --git a/libcxx/cmake/caches/Generic-hardening-mode-extensive.cmake b/libcxx/cmake/caches/Generic-hardening-mode-extensive.cmake
index 72263dfd84635..d4d506eba53f3 100644
--- a/libcxx/cmake/caches/Generic-hardening-mode-extensive.cmake
+++ b/libcxx/cmake/caches/Generic-hardening-mode-extensive.cmake
@@ -1 +1,3 @@
 set(LIBCXX_HARDENING_MODE "extensive" CACHE STRING "")
+set(LIBCXX_TEST_PARAMS "enable_modules=clang" CACHE STRING "")
+set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
diff --git a/libcxx/cmake/caches/Generic-hardening-mode-fast-with-abi-breaks.cmake b/libcxx/cmake/caches/Generic-hardening-mode-fast-with-abi-breaks.cmake
index d4ce32ce5b17f..2d617737e9635 100644
--- a/libcxx/cmake/caches/Generic-hardening-mode-fast-with-abi-breaks.cmake
+++ b/libcxx/cmake/caches/Generic-hardening-mode-fast-with-abi-breaks.cmake
@@ -8,3 +8,5 @@ set(_defines
     _LIBCPP_ABI_BOUNDED_ITERATORS_IN_OPTIONAL
 )
 set(LIBCXX_ABI_DEFINES "${_defines}" CACHE STRING "")
+set(LIBCXX_TEST_PARAMS "enable_modules=clang" CACHE STRING "")
+set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
diff --git a/libcxx/cmake/caches/Generic-hardening-mode-fast.cmake b/libcxx/cmake/caches/Generic-hardening-mode-fast.cmake
index cad5a1c4837fc..acc9cbd69afda 100644
--- a/libcxx/cmake/caches/Generic-hardening-mode-fast.cmake
+++ b/libcxx/cmake/caches/Generic-hardening-mode-fast.cmake
@@ -1 +1,3 @@
 set(LIBCXX_HARDENING_MODE "fast" CACHE STRING "")
+set(LIBCXX_TEST_PARAMS "enable_modules=clang" CACHE STRING "")
+set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
diff --git a/libcxx/cmake/caches/Generic-merged.cmake b/libcxx/cmake/caches/Generic-merged.cmake
index 7ebb8026236dd..461d10336e2fb 100644
--- a/libcxx/cmake/caches/Generic-merged.cmake
+++ b/libcxx/cmake/caches/Generic-merged.cmake
@@ -9,3 +9,6 @@ set(LIBCXXABI_ENABLE_STATIC_UNWINDER ON CACHE BOOL "")
 set(LIBCXXABI_STATICALLY_LINK_UNWINDER_IN_STATIC_LIBRARY ON CACHE BOOL "")
 
 set(LIBUNWIND_ENABLE_SHARED OFF CACHE BOOL "")
+
+set(LIBCXX_TEST_PARAMS "enable_modules=clang" CACHE STRING "")
+set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
diff --git a/libcxx/cmake/caches/Generic-msan.cmake b/libcxx/cmake/caches/Generic-msan.cmake
index a8fbd285a9adf..a7e3128399285 100644
--- a/libcxx/cmake/caches/Generic-msan.cmake
+++ b/libcxx/cmake/caches/Generic-msan.cmake
@@ -1,4 +1,4 @@
 set(LLVM_USE_SANITIZER "MemoryWithOrigins" CACHE STRING "")
-set(LIBCXX_TEST_PARAMS "long_tests=False" CACHE STRING "") # MSAN is really slow and tests can sometimes timeout otherwise
+set(LIBCXX_TEST_PARAMS "long_tests=False;enable_modules=clang" CACHE STRING "") # MSAN is really slow and tests can sometimes timeout otherwise
 set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
 set(LIBCXXABI_USE_LLVM_UNWINDER OFF CACHE BOOL "") # MSAN is compiled against the system unwinder, which leads to false positives
diff --git a/libcxx/cmake/caches/Generic-optimized-speed.cmake b/libcxx/cmake/caches/Generic-optimized-speed.cmake
index 577a5de9f34c5..b3a845caa0d54 100644
--- a/libcxx/cmake/caches/Generic-optimized-speed.cmake
+++ b/libcxx/cmake/caches/Generic-optimized-speed.cmake
@@ -2,3 +2,5 @@ set(CMAKE_BUILD_TYPE RelWithDebInfo CACHE STRING "")
 set(LIBCXX_TEST_PARAMS "optimization=speed" CACHE STRING "")
 set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
 set(LIBUNWIND_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
+set(LIBCXX_TEST_PARAMS "enable_modules=clang" CACHE STRING "")
+set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
diff --git a/libcxx/cmake/caches/Generic-static.cmake b/libcxx/cmake/caches/Generic-static.cmake
index ed2bf857146dc..0866a215b9507 100644
--- a/libcxx/cmake/caches/Generic-static.cmake
+++ b/libcxx/cmake/caches/Generic-static.cmake
@@ -1,3 +1,5 @@
 set(LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
 set(LIBCXXABI_ENABLE_SHARED OFF CACHE BOOL "")
 set(LIBUNWIND_ENABLE_SHARED OFF CACHE BOOL "")
+set(LIBCXX_TEST_PARAMS "enable_modules=clang" CACHE STRING "")
+set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
diff --git a/libcxx/cmake/caches/Generic-tsan.cmake b/libcxx/cmake/caches/Generic-tsan.cmake
index c42c1bb8e7222..662fb1f46ebe5 100644
--- a/libcxx/cmake/caches/Generic-tsan.cmake
+++ b/libcxx/cmake/caches/Generic-tsan.cmake
@@ -1,2 +1,4 @@
 set(LLVM_USE_SANITIZER "Thread" CACHE STRING "")
 set(LIBCXXABI_USE_LLVM_UNWINDER OFF CACHE BOOL "") # TSAN is compiled against the system unwinder, which leads to false positives
+set(LIBCXX_TEST_PARAMS "enable_modules=clang" CACHE STRING "")
+set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
diff --git a/libcxx/cmake/caches/Generic-ubsan.cmake b/libcxx/cmake/caches/Generic-ubsan.cmake
index 7ad891e4aed9e..f1a36c355b47c 100644
--- a/libcxx/cmake/caches/Generic-ubsan.cmake
+++ b/libcxx/cmake/caches/Generic-ubsan.cmake
@@ -1,2 +1,4 @@
 set(LLVM_USE_SANITIZER "Undefined" CACHE STRING "")
 set(LIBCXX_ABI_UNSTABLE ON CACHE BOOL "")
+set(LIBCXX_TEST_PARAMS "enable_modules=clang" CACHE STRING "")
+set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
diff --git a/libcxx/include/__flat_map/flat_map.h b/libcxx/include/__flat_map/flat_map.h
index 7bb235ba76503..159e652e1a326 100644
--- a/libcxx/include/__flat_map/flat_map.h
+++ b/libcxx/include/__flat_map/flat_map.h
@@ -47,6 +47,7 @@
 #include <__ranges/container_compatible_range.h>
 #include <__ranges/drop_view.h>
 #include <__ranges/from_range.h>
+#include <__ranges/range_adaptor.h>
 #include <__ranges/size.h>
 #include <__ranges/subrange.h>
 #include <__ranges/zip_view.h>
diff --git a/libcxx/include/__flat_map/flat_multimap.h b/libcxx/include/__flat_map/flat_multimap.h
index 96d945405cffe..6a608723da1ba 100644
--- a/libcxx/include/__flat_map/flat_multimap.h
+++ b/libcxx/include/__flat_map/flat_multimap.h
@@ -45,6 +45,7 @@
 #include <__ranges/container_compatible_range.h>
 #include <__ranges/drop_view.h>
 #include <__ranges/from_range.h>
+#include <__ranges/range_adaptor.h>
 #include <__ranges/size.h>
 #include <__ranges/subrange.h>
 #include <__ranges/zip_view.h>
diff --git a/libcxx/include/__flat_set/flat_multiset.h b/libcxx/include/__flat_set/flat_multiset.h
index 5cfa38fb41057..7be0b2d20c54d 100644
--- a/libcxx/include/__flat_set/flat_multiset.h
+++ b/libcxx/include/__flat_set/flat_multiset.h
@@ -40,6 +40,7 @@
 #include <__ranges/container_compatible_range.h>
 #include <__ranges/drop_view.h>
 #include <__ranges/from_range.h>
+#include <__ranges/range_adaptor.h>
 #include <__ranges/size.h>
 #include <__ranges/subrange.h>
 #include <__type_traits/container_traits.h>
diff --git a/libcxx/test/libcxx/containers/views/mdspan/layout_stride/assert.ctor.extents_span.non_unique.pass.cpp b/libcxx/test/libcxx/containers/views/mdspan/layout_stride/assert.ctor.extents_span.non_unique.pass.cpp
index fd0701e9ee3a7..ed2e475ccf022 100644
--- a/libcxx/test/libcxx/containers/views/mdspan/layout_stride/assert.ctor.extents_span.non_unique.pass.cpp
+++ b/libcxx/test/libcxx/containers/views/mdspan/layout_stride/assert.ctor.extents_span.non_unique.pass.cpp
@@ -30,8 +30,9 @@
 //
 // Effects: Direct-non-list-initializes extents_ with e, and for all d in the range [0, rank_), direct-non-list-initializes strides_[d] with as_const(s[d]).
 
-#include <mdspan>
 #include <cassert>
+#include <mdspan>
+#include <span>
 
 #include "check_assertion.h"
 
diff --git a/libcxx/test/libcxx/utilities/utility/__murmur2_or_cityhash.abi-v2.pass.cpp b/libcxx/test/libcxx/utilities/utility/__murmur2_or_cityhash.abi-v2.pass.cpp
index 25c0b9f177dce..6101f0ac75053 100644
--- a/libcxx/test/libcxx/utilities/utility/__murmur2_or_cityhash.abi-v2.pass.cpp
+++ b/libcxx/test/libcxx/utilities/utility/__murmur2_or_cityhash.abi-v2.pass.cpp
@@ -15,6 +15,7 @@
 // REQUIRES: libcpp-abi-version=2
 
 #include <cassert>
+#include <cstdint>
 #include <string>
 #include <utility>
 
diff --git a/libcxx/test/std/iterators/iterator.container/ssize.LWG3207.compile.pass.cpp b/libcxx/test/std/iterators/iterator.container/ssize.LWG3207.compile.pass.cpp
index e97020f9440ca..1ca68b15205e8 100644
--- a/libcxx/test/std/iterators/iterator.container/ssize.LWG3207.compile.pass.cpp
+++ b/libcxx/test/std/iterators/iterator.container/ssize.LWG3207.compile.pass.cpp
@@ -22,6 +22,7 @@
 #include <iterator>
 #include <climits>
 #include <cstddef>
+#include <cstdint>
 
 // Test the test:
 static_assert(sizeof(std::ptrdiff_t) == 4, "Run only on these platforms");