diff --git a/docs/markdown/snippets/cpp-debug.md b/docs/markdown/snippets/cpp-debug.md
new file mode 100644
index 000000000000..2a62b93994b4
--- /dev/null
+++ b/docs/markdown/snippets/cpp-debug.md
@@ -0,0 +1,10 @@
+## `ndebug` setting now controls C++ stdlib assertions
+
+The `ndebug` setting, if disabled, now passes preprocessor defines to enable
+debugging assertions within the C++ standard library.
+
+For GCC, `-D_GLIBCXX_ASSERTIONS=1` is set.
+
+For Clang, `-D_GLIBCXX_ASSERTIONS=1` is set to cover libstdc++ usage,
+and `-D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_EXTENSIVE` or
+`-D_LIBCPP_ENABLE_ASSERTIONS=1` is used depending on the Clang version.
diff --git a/mesonbuild/compilers/cpp.py b/mesonbuild/compilers/cpp.py
index 226605390356..f6a03caf218b 100644
--- a/mesonbuild/compilers/cpp.py
+++ b/mesonbuild/compilers/cpp.py
@@ -293,6 +293,20 @@ def get_option_link_args(self, options: 'KeyedOptionDictType') -> T.List[str]:
             return libs
         return []
 
+    def get_assert_args(self, disable: bool) -> T.List[str]:
+        args: T.List[str] = []
+        if disable:
+            return ['-DNDEBUG']
+
+        # Clang supports both libstdc++ and libc++
+        args.append('-D_GLIBCXX_ASSERTIONS=1')
+        if version_compare(self.version, '>=18'):
+            args.append('-D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_EXTENSIVE')
+        elif version_compare(self.version, '>=15'):
+            args.append('-D_LIBCPP_ENABLE_ASSERTIONS=1')
+
+        return args
+
 
 class ArmLtdClangCPPCompiler(ClangCPPCompiler):
 
@@ -462,6 +476,14 @@ def get_option_link_args(self, options: 'KeyedOptionDictType') -> T.List[str]:
             return libs
         return []
 
+    def get_assert_args(self, disable: bool) -> T.List[str]:
+        if disable:
+            return ['-DNDEBUG']
+
+        # XXX: This needs updating if/when GCC starts to support libc++.
+        # It currently only does so via an experimental configure arg.
+        return ['-D_GLIBCXX_ASSERTIONS=1']
+
     def get_pch_use_args(self, pch_dir: str, header: str) -> T.List[str]:
         return ['-fpch-preprocess', '-include', os.path.basename(header)]