diff --git a/libc/src/assert/CMakeLists.txt b/libc/src/assert/CMakeLists.txt
--- a/libc/src/assert/CMakeLists.txt
+++ b/libc/src/assert/CMakeLists.txt
@@ -3,6 +3,7 @@
   SRCS
     __assert_fail.cpp
   HDRS
+    __assert_fail.h
     assert.h
   DEPENDS
     # These two dependencies are temporary and should be replaced by fprintf
diff --git a/libc/src/assert/__assert_fail.h b/libc/src/assert/__assert_fail.h
new file mode 100644
--- /dev/null
+++ b/libc/src/assert/__assert_fail.h
@@ -0,0 +1,21 @@
+//===-- Internal header for __assert_fail -----------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_ASSERT_ASSERT_FAIL_H
+#define LLVM_LIBC_SRC_ASSERT_ASSERT_FAIL_H
+
+#include <stddef.h>
+
+namespace __llvm_libc {
+
+[[noreturn]] void __assert_fail(const char *assertion, const char *file,
+                                unsigned line, const char *function);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_ASSERT_ASSERT_FAIL_H
diff --git a/libc/src/assert/__assert_fail.cpp b/libc/src/assert/__assert_fail.cpp
--- a/libc/src/assert/__assert_fail.cpp
+++ b/libc/src/assert/__assert_fail.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "src/assert/assert.h"
+#include "src/assert/__assert_fail.h"
 #include "src/stdlib/abort.h"
 
 // These includes are temporary.
diff --git a/libc/src/assert/assert.h b/libc/src/assert/assert.h
--- a/libc/src/assert/assert.h
+++ b/libc/src/assert/assert.h
@@ -6,19 +6,11 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_LIBC_SRC_ASSERT_ASSERT_H
-#define LLVM_LIBC_SRC_ASSERT_ASSERT_H
+#include "src/assert/__assert_fail.h"
 
-#include <stddef.h>
-
-namespace __llvm_libc {
-
-[[noreturn]] void __assert_fail(const char *assertion, const char *file, unsigned line,
-                  const char *function);
-
-} // namespace __llvm_libc
-
-#endif // LLVM_LIBC_SRC_ASSERT_ASSERT_H
+// There is no header guard here since assert is intended to be able to be
+// able to be included multiple times with NDEBUG defined differently, causing
+// different behavior.
 
 #undef assert
 
diff --git a/libc/src/errno/CMakeLists.txt b/libc/src/errno/CMakeLists.txt
--- a/libc/src/errno/CMakeLists.txt
+++ b/libc/src/errno/CMakeLists.txt
@@ -1,7 +1,8 @@
 add_entrypoint_object(
   __errno_location
   SRCS
-    errno_location.cpp
+    __errno_location.cpp
   HDRS
+    __errno_location.h
     llvmlibc_errno.h
 )
diff --git a/libc/src/errno/llvmlibc_errno.h b/libc/src/errno/__errno_location.h
copy from libc/src/errno/llvmlibc_errno.h
copy to libc/src/errno/__errno_location.h
--- a/libc/src/errno/llvmlibc_errno.h
+++ b/libc/src/errno/__errno_location.h
@@ -1,4 +1,4 @@
-//===-- Implementation header for errno -------------------------*- C++ -*-===//
+//===-- Implementation header for __errno_location --------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,12 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_LIBC_SRC_ERRNO_LLVMLIBC_ERRNO_H
-#define LLVM_LIBC_SRC_ERRNO_LLVMLIBC_ERRNO_H
-
-// Internal code should use this and not use the errno macro from the
-// public header.
-#define llvmlibc_errno (*__llvm_libc::__errno_location())
+#ifndef LLVM_LIBC_SRC_ERRNO_ERRNO_LOCATION_H
+#define LLVM_LIBC_SRC_ERRNO_ERRNO_LOCATION_H
 
 namespace __llvm_libc {
 
@@ -19,4 +15,4 @@
 
 } // namespace __llvm_libc
 
-#endif // LLVM_LIBC_SRC_ERRNO_LLVMLIBC_ERRNO_H
+#endif // LLVM_LIBC_SRC_ERRNO_ERRNO_LOCATION_H
diff --git a/libc/src/errno/errno_location.cpp b/libc/src/errno/__errno_location.cpp
rename from libc/src/errno/errno_location.cpp
rename to libc/src/errno/__errno_location.cpp
--- a/libc/src/errno/errno_location.cpp
+++ b/libc/src/errno/__errno_location.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "src/errno/llvmlibc_errno.h"
+#include "src/errno/__errno_location.h"
 
 #include "src/__support/common.h"
 
diff --git a/libc/src/errno/llvmlibc_errno.h b/libc/src/errno/llvmlibc_errno.h
--- a/libc/src/errno/llvmlibc_errno.h
+++ b/libc/src/errno/llvmlibc_errno.h
@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "src/errno/__errno_location.h"
+
 #ifndef LLVM_LIBC_SRC_ERRNO_LLVMLIBC_ERRNO_H
 #define LLVM_LIBC_SRC_ERRNO_LLVMLIBC_ERRNO_H
 
@@ -13,10 +15,4 @@
 // public header.
 #define llvmlibc_errno (*__llvm_libc::__errno_location())
 
-namespace __llvm_libc {
-
-int *__errno_location();
-
-} // namespace __llvm_libc
-
 #endif // LLVM_LIBC_SRC_ERRNO_LLVMLIBC_ERRNO_H