diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
index 1423b6713fd35..fabfb126d06f3 100644
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -298,6 +298,7 @@ endif()
 
 # Feature options -------------------------------------------------------------
 option(LIBCXX_HAS_MUSL_LIBC "Build libc++ with support for the Musl C library" OFF)
+option(LIBCXX_HAS_NEWLIB_LIBC "Build libc++ with support for the Newlib C library" OFF)
 option(LIBCXX_HAS_PTHREAD_API "Ignore auto-detection and force use of pthread API" OFF)
 option(LIBCXX_HAS_WIN32_THREAD_API "Ignore auto-detection and force use of win32 thread API" OFF)
 option(LIBCXX_HAS_EXTERNAL_THREAD_API
@@ -754,6 +755,7 @@ config_define(${LIBCXX_HAS_PTHREAD_API} _LIBCPP_HAS_THREAD_API_PTHREAD)
 config_define(${LIBCXX_HAS_EXTERNAL_THREAD_API} _LIBCPP_HAS_THREAD_API_EXTERNAL)
 config_define(${LIBCXX_HAS_WIN32_THREAD_API} _LIBCPP_HAS_THREAD_API_WIN32)
 config_define(${LIBCXX_HAS_MUSL_LIBC} _LIBCPP_HAS_MUSL_LIBC)
+config_define(${LIBCXX_HAS_NEWLIB_LIBC} _LIBCPP_HAS_NEWLIB_LIBC)
 config_define_if(LIBCXX_NO_VCRUNTIME _LIBCPP_NO_VCRUNTIME)
 config_define(${LIBCXX_ENABLE_FILESYSTEM} _LIBCPP_HAS_FILESYSTEM)
 config_define(${LIBCXX_ENABLE_RANDOM_DEVICE} _LIBCPP_HAS_RANDOM_DEVICE)
diff --git a/libcxx/include/__config_site.in b/libcxx/include/__config_site.in
index 6dcca1849a96c..6521cf7c51c96 100644
--- a/libcxx/include/__config_site.in
+++ b/libcxx/include/__config_site.in
@@ -17,6 +17,7 @@
 #cmakedefine01 _LIBCPP_HAS_MONOTONIC_CLOCK
 #cmakedefine01 _LIBCPP_HAS_TERMINAL
 #cmakedefine01 _LIBCPP_HAS_MUSL_LIBC
+#cmakedefine01 _LIBCPP_HAS_NEWLIB_LIBC
 #cmakedefine01 _LIBCPP_HAS_THREAD_API_PTHREAD
 #cmakedefine01 _LIBCPP_HAS_THREAD_API_EXTERNAL
 #cmakedefine01 _LIBCPP_HAS_THREAD_API_WIN32
diff --git a/libcxx/include/__fwd/ios.h b/libcxx/include/__fwd/ios.h
index 831624f4b1c57..96505e615693c 100644
--- a/libcxx/include/__fwd/ios.h
+++ b/libcxx/include/__fwd/ios.h
@@ -31,7 +31,7 @@ using wios = basic_ios<wchar_t>;
 template <class _CharT, class _Traits>
 class _LIBCPP_PREFERRED_NAME(ios) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wios)) basic_ios;
 
-#if defined(_NEWLIB_VERSION)
+#if _LIBCPP_HAS_NEWLIB_LIBC
 // On newlib, off_t is 'long int'
 using streamoff = long int; // for char_traits in <string>
 #else
diff --git a/libcxx/utils/ci/run-buildbot b/libcxx/utils/ci/run-buildbot
index 7442361627104..b04e3eed203f1 100755
--- a/libcxx/utils/ci/run-buildbot
+++ b/libcxx/utils/ci/run-buildbot
@@ -205,6 +205,7 @@ function test-armv7m-picolibc() {
         -DLIBUNWIND_TEST_CONFIG="armv7m-picolibc-libunwind.cfg.in" \
         -DCMAKE_C_FLAGS="${flags}" \
         -DCMAKE_CXX_FLAGS="${flags}" \
+        -DLIBCXX_HAS_NEWLIB_LIBC=ON \
         "${@}"
 
     step "Installing compiler-rt"