diff --git a/libc/hdr/fcntl_overlay.h b/libc/hdr/fcntl_overlay.h
index c1cc98b0ebb2..17ae78b3d0ec 100644
--- a/libc/hdr/fcntl_overlay.h
+++ b/libc/hdr/fcntl_overlay.h
@@ -20,6 +20,11 @@
 // `__USE_FORTIFY_LEVEL`, which will be temporarily disabled
 // with `_FORTIFY_SOURCE`.
 
+#ifdef _FORTIFY_SOURCE
+#define LIBC_OLD_FORTIFY_SOURCE _FORTIFY_SOURCE
+#undef _FORTIFY_SOURCE
+#endif
+
 #ifdef __USE_FORTIFY_LEVEL
 #define LIBC_OLD_USE_FORTIFY_LEVEL __USE_FORTIFY_LEVEL
 #undef __USE_FORTIFY_LEVEL
@@ -28,6 +33,11 @@
 
 #include <fcntl.h>
 
+#ifdef LIBC_OLD_FORTIFY_SOURCE
+#define _FORTIFY_SOURCE LIBC_OLD_FORTIFY_SOURCE
+#undef LIBC_OLD_FORTIFY_SOURCE
+#endif
+
 #ifdef LIBC_OLD_USE_FORTIFY_LEVEL
 #undef __USE_FORTIFY_LEVEL
 #define __USE_FORTIFY_LEVEL LIBC_OLD_USE_FORTIFY_LEVEL
diff --git a/libc/hdr/types/CMakeLists.txt b/libc/hdr/types/CMakeLists.txt
index c4d14e6f8931..68a0e9603f97 100644
--- a/libc/hdr/types/CMakeLists.txt
+++ b/libc/hdr/types/CMakeLists.txt
@@ -51,6 +51,8 @@ add_proxy_header_library(
   struct_flock
   HDRS
     struct_flock.h
+  DEPENDS
+    libc.hdr.fcntl_overlay
   FULL_BUILD_DEPENDS
     libc.include.llvm-libc-types.struct_flock
 )
@@ -59,6 +61,8 @@ add_proxy_header_library(
   struct_flock64
   HDRS
     struct_flock64.h
+  DEPENDS
+    libc.hdr.fcntl_overlay
   FULL_BUILD_DEPENDS
     libc.include.llvm-libc-types.struct_flock64
 )
@@ -67,6 +71,8 @@ add_proxy_header_library(
   struct_f_owner_ex
   HDRS
     struct_f_owner_ex.h
+  DEPENDS
+    libc.hdr.fcntl_overlay
   FULL_BUILD_DEPENDS
     libc.include.llvm-libc-types.struct_f_owner_ex
 )
diff --git a/libc/hdr/types/struct_f_owner_ex.h b/libc/hdr/types/struct_f_owner_ex.h
index 49985115ae4b..6e37cea6df84 100644
--- a/libc/hdr/types/struct_f_owner_ex.h
+++ b/libc/hdr/types/struct_f_owner_ex.h
@@ -14,7 +14,7 @@
 
 #else
 
-#include <fcntl.h>
+#include "hdr/fcntl_overlay.h"
 
 #endif // LIBC_FULL_BUILD
 
diff --git a/libc/hdr/types/struct_flock.h b/libc/hdr/types/struct_flock.h
index a552b91c432b..6a6c928e6fa6 100644
--- a/libc/hdr/types/struct_flock.h
+++ b/libc/hdr/types/struct_flock.h
@@ -14,7 +14,7 @@
 
 #else
 
-#include <fcntl.h>
+#include "hdr/fcntl_overlay.h"
 
 #endif // LIBC_FULL_BUILD
 
diff --git a/libc/hdr/types/struct_flock64.h b/libc/hdr/types/struct_flock64.h
index 84fe67816c33..fcfda59479a2 100644
--- a/libc/hdr/types/struct_flock64.h
+++ b/libc/hdr/types/struct_flock64.h
@@ -14,7 +14,7 @@
 
 #else
 
-#include <fcntl.h>
+#include "hdr/fcntl_overlay.h"
 
 #endif // LIBC_FULL_BUILD