diff --git a/libc/config/gpu/api.td b/libc/config/gpu/api.td
--- a/libc/config/gpu/api.td
+++ b/libc/config/gpu/api.td
@@ -2,17 +2,6 @@
 
 include "spec/stdc.td"
 
-def NullMacro : MacroDef<"NULL"> {
-  let Defn = [{
-    #define __need_NULL
-    #include <stddef.h>
-  }];
-}
-
 def StringAPI : PublicAPI<"string.h"> {
   let Types = ["size_t"];
-
-  let Macros = [
-    NullMacro,
-  ];
 }
diff --git a/libc/config/linux/api.td b/libc/config/linux/api.td
--- a/libc/config/linux/api.td
+++ b/libc/config/linux/api.td
@@ -36,13 +36,6 @@
   }];
 }
 
-def NullMacro : MacroDef<"NULL"> {
-  let Defn = [{
-    #define __need_NULL
-    #include <stddef.h>
-  }];
-}
-
 def AssertAPI : PublicAPI<"assert.h"> {
   let Macros = [
     AssertMacro,
@@ -134,10 +127,6 @@
 
 def StringAPI : PublicAPI<"string.h"> {
   let Types = ["size_t"];
-
-  let Macros = [
-    NullMacro,
-  ];
 }
 
 def StdIOAPI : PublicAPI<"stdio.h"> {
diff --git a/libc/include/CMakeLists.txt b/libc/include/CMakeLists.txt
--- a/libc/include/CMakeLists.txt
+++ b/libc/include/CMakeLists.txt
@@ -91,6 +91,7 @@
   GEN_HDR string.h
   DEPENDS
     .llvm_libc_common_h
+    .llvm-libc-macros.null_macro
     .llvm-libc-types.size_t
 )
 
diff --git a/libc/include/llvm-libc-macros/CMakeLists.txt b/libc/include/llvm-libc-macros/CMakeLists.txt
--- a/libc/include/llvm-libc-macros/CMakeLists.txt
+++ b/libc/include/llvm-libc-macros/CMakeLists.txt
@@ -6,6 +6,12 @@
     generic-error-number-macros.h
 )
 
+add_header(
+  null_macro
+  HDR
+    null-macro.h
+)
+
 add_header(
   fcntl_macros
   HDR
diff --git a/libc/include/string.h.def b/libc/include/llvm-libc-macros/null-macro.h
copy from libc/include/string.h.def
copy to libc/include/llvm-libc-macros/null-macro.h
--- a/libc/include/string.h.def
+++ b/libc/include/llvm-libc-macros/null-macro.h
@@ -1,4 +1,4 @@
-//===-- C standard library header string.h --------------------------------===//
+//===-- Definition of the NULL macro --------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,11 +6,10 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_LIBC_STRING_H
-#define LLVM_LIBC_STRING_H
+#ifndef __LLVM_LIBC_MACROS_NULL_MACRO_H
+#define __LLVM_LIBC_MACROS_NULL_MACRO_H
 
-#include <__llvm-libc-common.h>
+#define __need_NULL
+#include <stddef.h>
 
-%%public_api()
-
-#endif // LLVM_LIBC_STRING_H
+#endif // __LLVM_LIBC_MACROS_NULL_MACRO_H
diff --git a/libc/include/string.h.def b/libc/include/string.h.def
--- a/libc/include/string.h.def
+++ b/libc/include/string.h.def
@@ -11,6 +11,8 @@
 
 #include <__llvm-libc-common.h>
 
+#include <llvm-libc-macros/null-macro.h>
+
 %%public_api()
 
 #endif // LLVM_LIBC_STRING_H