diff --git a/include/__debug b/include/__debug
index e67dd08..e3a5ec9 100644
--- a/include/__debug
+++ b/include/__debug
@@ -17,13 +17,16 @@
 #pragma GCC system_header
 #endif
 
-#if _LIBCPP_DEBUG_LEVEL >= 1
+#if _LIBCPP_DEBUG_LEVEL >= 1 || defined(_LIBCPP_BUILDING_LIBRARY)
 #   include <cstdlib>
 #   include <cstdio>
 #   include <cstddef>
-#   ifndef _LIBCPP_ASSERT
-#      define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : (_VSTD::fprintf(stderr, "%s\n", m), _VSTD::abort()))
-#   endif
+#   include <exception>
+#endif
+
+#if _LIBCPP_DEBUG_LEVEL >= 1 && !defined(_LIBCPP_ASSERT)
+# define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : \
+  _VSTD::__libcpp_debug_function(_VSTD::__libcpp_debug_info{__FILE__, __LINE__, #x, m}))
 #endif
 
 #if _LIBCPP_DEBUG_LEVEL >= 2
@@ -43,10 +46,61 @@
 #define _LIBCPP_DEBUG_MODE(...) ((void)0)
 #endif
 
-#if _LIBCPP_DEBUG_LEVEL >= 2
+#if _LIBCPP_DEBUG_LEVEL < 1
+class _LIBCPP_EXCEPTION_ABI __libcpp_debug_exception;
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+struct _LIBCPP_TYPE_VIS_ONLY __libcpp_debug_info {
+  const char* __file_;
+  int __line_;
+  const char* __pred_;
+  const char* __msg_;
+};
+
+/// __libcpp_debug_function_type - The type of the assertion failure handler.
+typedef void(*__libcpp_debug_function_type)(__libcpp_debug_info const&);
+
+/// __libcpp_debug_function - The handler function called when a _LIBCPP_ASSERT
+///    fails.
+extern __libcpp_debug_function_type __libcpp_debug_function;
+
+/// __libcpp_abort_debug_function - A debug handler that aborts when called.
+_LIBCPP_NORETURN _LIBCPP_FUNC_VIS
+void __libcpp_abort_debug_function(__libcpp_debug_info const&);
+
+/// __libcpp_throw_debug_function - A debug handler that throws
+///   an instance of __libcpp_debug_exception when called.
+ _LIBCPP_NORETURN _LIBCPP_FUNC_VIS
+void __libcpp_throw_debug_function(__libcpp_debug_info const&);
+
+/// __libcpp_set_debug_function - Set the debug handler to the specified
+///    function.
+_LIBCPP_FUNC_VIS
+bool __libcpp_set_debug_function(__libcpp_debug_function_type __func);
+
+// Setup the throwing debug handler during dynamic initialization.
+#if _LIBCPP_DEBUG_LEVEL >= 1 && defined(_LIBCPP_DEBUG_USE_EXCEPTIONS)
+static bool __init_dummy = __libcpp_set_debug_function(__libcpp_throw_debug_function);
+#endif
+
+#if _LIBCPP_DEBUG_LEVEL >= 1 || defined(_LIBCPP_BUILDING_LIBRARY)
+class _LIBCPP_EXCEPTION_ABI __libcpp_debug_exception : public exception {
+public:
+  __libcpp_debug_exception() _NOEXCEPT;
+  explicit __libcpp_debug_exception(__libcpp_debug_info const& __i);
+  __libcpp_debug_exception(__libcpp_debug_exception const&);
+  ~__libcpp_debug_exception() _NOEXCEPT;
+  const char* what() const _NOEXCEPT;
+private:
+  struct __libcpp_debug_exception_imp;
+  __libcpp_debug_exception_imp *__imp_;
+};
+#endif
+
+#if _LIBCPP_DEBUG_LEVEL >= 2 || defined(_LIBCPP_BUILDING_LIBRARY)
+
 struct _LIBCPP_TYPE_VIS __c_node;
 
 struct _LIBCPP_TYPE_VIS __i_node
@@ -115,7 +169,7 @@
 };
 
 template <class _Cont>
-bool
+inline bool
 _C_node<_Cont>::__dereferenceable(const void* __i) const
 {
     typedef typename _Cont::const_iterator iterator;
@@ -125,7 +179,7 @@
 }
 
 template <class _Cont>
-bool
+inline bool
 _C_node<_Cont>::__decrementable(const void* __i) const
 {
     typedef typename _Cont::const_iterator iterator;
@@ -135,7 +189,7 @@
 }
 
 template <class _Cont>
-bool
+inline bool
 _C_node<_Cont>::__addable(const void* __i, ptrdiff_t __n) const
 {
     typedef typename _Cont::const_iterator iterator;
@@ -145,7 +199,7 @@
 }
 
 template <class _Cont>
-bool
+inline bool
 _C_node<_Cont>::__subscriptable(const void* __i, ptrdiff_t __n) const
 {
     typedef typename _Cont::const_iterator iterator;
@@ -227,9 +281,9 @@
 _LIBCPP_FUNC_VIS const __libcpp_db* __get_const_db();
 
 
-_LIBCPP_END_NAMESPACE_STD
+#endif // _LIBCPP_DEBUG_LEVEL >= 2 || defined(_LIBCPP_BUILDING_LIBRARY)
 
-#endif
+_LIBCPP_END_NAMESPACE_STD
 
 #endif  // _LIBCPP_DEBUG_H