diff --git a/mlibc/include/alloca.h b/mlibc/include/alloca.h
index a3883b8c..61df8930 100644
--- a/mlibc/include/alloca.h
+++ b/mlibc/include/alloca.h
@@ -24,6 +24,7 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #endif
+#undef __MES_ALLOCA_H 1
 #include_next <alloca.h>
 
 #else // ! (__GNUC__ && POSIX)
diff --git a/mlibc/include/assert.h b/mlibc/include/assert.h
index d301c196..18ce042c 100644
--- a/mlibc/include/assert.h
+++ b/mlibc/include/assert.h
@@ -24,6 +24,7 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #endif
+#undef __MES_ASSERT_H
 #include_next <assert.h>
 #else // ! (__GNUC__ && POSIX)
 #define assert(x) ((x) ? (void)0 : assert_fail (#x))
diff --git a/mlibc/include/ctype.h b/mlibc/include/ctype.h
index 722814c9..32be3c50 100644
--- a/mlibc/include/ctype.h
+++ b/mlibc/include/ctype.h
@@ -24,6 +24,7 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #endif
+#undef __MES_CTYPE_H
 #include_next <ctype.h>
 
 #else // ! (__GNUC__ && POSIX)
diff --git a/mlibc/include/dlfcn.h b/mlibc/include/dlfcn.h
index 254a2377..01c50fa1 100644
--- a/mlibc/include/dlfcn.h
+++ b/mlibc/include/dlfcn.h
@@ -21,6 +21,7 @@
 #define __MES_DLFCN_H 1
 
 #if __GNUC__ && POSIX
+#undef __MES_DLFCN_H
 #include_next <dlfcn.h>
 #endif // (__GNUC__ && POSIX)
 
diff --git a/mlibc/include/errno.h b/mlibc/include/errno.h
index 3ffd1a08..ca279261 100644
--- a/mlibc/include/errno.h
+++ b/mlibc/include/errno.h
@@ -24,6 +24,7 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #endif
+#undef __MES_ERRNO_H
 #include_next <errno.h>
 #endif // ! (__GNUC__ && POSIX)
 
diff --git a/mlibc/include/fcntl.h b/mlibc/include/fcntl.h
index c728f8a6..7d30a7bb 100644
--- a/mlibc/include/fcntl.h
+++ b/mlibc/include/fcntl.h
@@ -24,6 +24,7 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #endif
+#undef __MES_FCNTL_H
 #include_next <fcntl.h>
 
 #else // ! (__GNUC__ && POSIX)
diff --git a/mlibc/include/features.h b/mlibc/include/features.h
index d4cbf27a..a75a698f 100644
--- a/mlibc/include/features.h
+++ b/mlibc/include/features.h
@@ -21,6 +21,7 @@
 #define __MES_FEATURES_H 1
 
 #if __GNUC__ && POSIX
+#undef __MES_FEATURES_H
 #include_next <features.h>
 #endif // (__GNUC__ && POSIX)
 
diff --git a/mlibc/include/inttypes.h b/mlibc/include/inttypes.h
index b3aa6107..b3f4f7e0 100644
--- a/mlibc/include/inttypes.h
+++ b/mlibc/include/inttypes.h
@@ -24,6 +24,7 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #endif
+#undef __MES_INTTYPES_H
 #include_next <inttypes.h>
 #else // ! (__GNUC__ && POSIX)
 
diff --git a/mlibc/include/libgen.h b/mlibc/include/libgen.h
index e5199cc0..2bad446b 100644
--- a/mlibc/include/libgen.h
+++ b/mlibc/include/libgen.h
@@ -24,6 +24,7 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #endif
+#undef __MES_LIBGEN_H
 #include_next <libgen.h>
 
 #else // ! (__GNUC__ && POSIX)
diff --git a/mlibc/include/limits.h b/mlibc/include/limits.h
index e4ec62cc..765dd4a8 100644
--- a/mlibc/include/limits.h
+++ b/mlibc/include/limits.h
@@ -24,6 +24,7 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #endif
+#undef __MES_LIMITS_H
 #include_next <limits.h>
 
 #else // ! (__GNUC__ && POSIX)
diff --git a/mlibc/include/locale.h b/mlibc/include/locale.h
index 6cfc027c..bbd07973 100644
--- a/mlibc/include/locale.h
+++ b/mlibc/include/locale.h
@@ -24,6 +24,7 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #endif
+#undef __MES_LOCALE_H
 #include_next <locale.h>
 
 #else // ! (__GNUC__ && POSIX)
diff --git a/mlibc/include/math.h b/mlibc/include/math.h
index 15dec7ca..c74b8864 100644
--- a/mlibc/include/math.h
+++ b/mlibc/include/math.h
@@ -21,6 +21,7 @@
 #define __MES_MATH_H 1
 
 #if __GNUC__ && POSIX
+#undef __MES_MATH_H
 #include_next <math.h>
 #endif // (__GNUC__ && POSIX)
 
diff --git a/mlibc/include/setjmp.h b/mlibc/include/setjmp.h
index e28153f8..2792ed0c 100644
--- a/mlibc/include/setjmp.h
+++ b/mlibc/include/setjmp.h
@@ -21,6 +21,7 @@
 #define __MES_SETJMP_H 1
 
 #if __GNUC__ && POSIX
+#undef __MES_SETJMP_H
 #include_next <setjmp.h>
 #else // ! (__GNUC__ && POSIX)
 
diff --git a/mlibc/include/signal.h b/mlibc/include/signal.h
index 50837dcd..d073a6b9 100644
--- a/mlibc/include/signal.h
+++ b/mlibc/include/signal.h
@@ -21,6 +21,7 @@
 #define __MES_SIGNAL_H 1
 
 #if __GNUC__ && POSIX
+#undef __MES_SIGNAL_H
 #include_next <signal.h>
 #endif // (__GNUC__ && POSIX)
 
diff --git a/mlibc/include/stdarg.h b/mlibc/include/stdarg.h
index 24df07fc..d2b16dfb 100644
--- a/mlibc/include/stdarg.h
+++ b/mlibc/include/stdarg.h
@@ -21,6 +21,7 @@
 #define __MES_STDARG_H 1
 
 #if __GNUC__ && POSIX
+#undef __MES_STDARG_H
 #include_next <stdarg.h>
 #else // ! (__GNUC__ && POSIX)
 
diff --git a/mlibc/include/stdbool.h b/mlibc/include/stdbool.h
index e2e1ee57..c900fc5b 100644
--- a/mlibc/include/stdbool.h
+++ b/mlibc/include/stdbool.h
@@ -24,6 +24,7 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #endif
+#undef __MES_STDBOOL_H
 #include_next <stdbool.h>
 
 #else // ! (__GNUC__ && POSIX)
diff --git a/mlibc/include/stdint.h b/mlibc/include/stdint.h
index e7f13fd0..a182bf65 100644
--- a/mlibc/include/stdint.h
+++ b/mlibc/include/stdint.h
@@ -24,6 +24,7 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #endif
+#undef __MES_STDINT_H
 #include_next <stdint.h>
 
 #else // ! (__GNUC__ && POSIX)
diff --git a/mlibc/include/stdio.h b/mlibc/include/stdio.h
index b9453a21..ada3909d 100644
--- a/mlibc/include/stdio.h
+++ b/mlibc/include/stdio.h
@@ -37,6 +37,7 @@ int sprintf (char *str, char const* format, ...);
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #endif
+#undef __MES_STDIO_H
 #include_next <stdio.h>
 
 int fdputs (char const* s, int fd);
diff --git a/mlibc/include/stdlib.h b/mlibc/include/stdlib.h
index ebaba062..b2d181bb 100644
--- a/mlibc/include/stdlib.h
+++ b/mlibc/include/stdlib.h
@@ -24,6 +24,7 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #endif
+#undef __MES_STDLIB_H
 #include_next <stdlib.h>
 #else  // !(__GNUC__ && POSIX)
 
diff --git a/mlibc/include/stdnoreturn.h b/mlibc/include/stdnoreturn.h
index 84a1e94b..e1e94fdb 100644
--- a/mlibc/include/stdnoreturn.h
+++ b/mlibc/include/stdnoreturn.h
@@ -24,6 +24,7 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #endif
+#undef __MES_STDNORETURN_H
 #include_next <stdnoreturn.h>
 
 #else // ! (__GNUC__ && POSIX)
diff --git a/mlibc/include/string.h b/mlibc/include/string.h
index 104a359d..c9c9f435 100644
--- a/mlibc/include/string.h
+++ b/mlibc/include/string.h
@@ -24,6 +24,7 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #endif
+#undef __MES_STRING_H
 #include_next <string.h>
 
 #else // ! (__GNUC__ && POSIX)
diff --git a/mlibc/include/strings.h b/mlibc/include/strings.h
index 0878530e..49b8f744 100644
--- a/mlibc/include/strings.h
+++ b/mlibc/include/strings.h
@@ -21,6 +21,7 @@
 #define __MES_STRINGS_H 1
 
 #if __GNUC__ && POSIX
+#undef __MES_STRINGS_H
 #include_next <strings.h>
 #endif // (__GNUC__ && POSIX)
 
diff --git a/mlibc/include/sys/cdefs.h b/mlibc/include/sys/cdefs.h
index 63c7dfa7..b156e084 100644
--- a/mlibc/include/sys/cdefs.h
+++ b/mlibc/include/sys/cdefs.h
@@ -21,6 +21,7 @@
 #define __MES_SYS_CDEFS_H 1
 
 #if __GNUC__ && POSIX
+#undef __MES_SYS_CDEFS_H
 #include_next <sys/cdefs.h>
 #endif // (__GNUC__ && POSIX)
 
diff --git a/mlibc/include/sys/mman.h b/mlibc/include/sys/mman.h
index 522a710a..93dff0ab 100644
--- a/mlibc/include/sys/mman.h
+++ b/mlibc/include/sys/mman.h
@@ -21,6 +21,7 @@
 #define __MES_SYS_MMAN_H 1
 
 #if __GNUC__ && POSIX
+#undef __MES_SYS_MMAN_H
 #include_next <sys/mman.h>
 #endif // (__GNUC__ && POSIX)
 
diff --git a/mlibc/include/sys/stat.h b/mlibc/include/sys/stat.h
index 6adae743..22ae8262 100644
--- a/mlibc/include/sys/stat.h
+++ b/mlibc/include/sys/stat.h
@@ -21,6 +21,7 @@
 #define __MES_SYS_STAT_H 1
 
 #if __GNUC__ && POSIX
+#undef __MES_SYS_STAT_H
 #include_next <sys/stat.h>
 #endif // (__GNUC__ && POSIX)
 
diff --git a/mlibc/include/sys/time.h b/mlibc/include/sys/time.h
index de788912..673cf56c 100644
--- a/mlibc/include/sys/time.h
+++ b/mlibc/include/sys/time.h
@@ -21,6 +21,7 @@
 #define __MES_SYS_TIME_H 1
 
 #if __GNUC__ && POSIX
+#undef __MES_SYS_TIME_H
 #include_next <sys/time.h>
 #endif // (__GNUC__ && POSIX)
 
diff --git a/mlibc/include/sys/timeb.h b/mlibc/include/sys/timeb.h
index 2cd99087..a2bacd3c 100644
--- a/mlibc/include/sys/timeb.h
+++ b/mlibc/include/sys/timeb.h
@@ -21,6 +21,7 @@
 #define __MES_SYS_TIMEB_H 1
 
 #if __GNUC__ && POSIX
+#undef __MES_SYS_TIMEB_H
 #include_next <sys/timeb.h>
 #endif // (__GNUC__ && POSIX)
 
diff --git a/mlibc/include/sys/types.h b/mlibc/include/sys/types.h
index b7b05c67..d2f1620c 100644
--- a/mlibc/include/sys/types.h
+++ b/mlibc/include/sys/types.h
@@ -21,6 +21,7 @@
 #define __MES_SYS_TYPES_H 1
 
 #if __GNUC__ && POSIX
+#undef __MES_SYS_TYPES_H
 #include_next <sys/types.h>
 #endif // (__GNUC__ && POSIX)
 
diff --git a/mlibc/include/sys/ucontext.h b/mlibc/include/sys/ucontext.h
index bdf9274f..4f68f36e 100644
--- a/mlibc/include/sys/ucontext.h
+++ b/mlibc/include/sys/ucontext.h
@@ -21,6 +21,7 @@
 #define __MES_SYS_UCONTEXT_H 1
 
 #if __GNUC__ && POSIX
+#undef __MES_SYS_UCONTEXT_H
 #include_next <sys/ucontext.h>
 #endif // (__GNUC__ && POSIX)
 
diff --git a/mlibc/include/sys/wait.h b/mlibc/include/sys/wait.h
index 7e28e89f..6d5eb524 100644
--- a/mlibc/include/sys/wait.h
+++ b/mlibc/include/sys/wait.h
@@ -21,6 +21,7 @@
 #define __MES_SYS_WAIT_H 1
 
 #if __GNUC__ && POSIX
+#undef __MES_SYS_WAIT_H
 #include_next <sys/wait.h>
 #endif // (__GNUC__ && POSIX)
 
diff --git a/mlibc/include/time.h b/mlibc/include/time.h
index 1406d5b5..0b80ee97 100644
--- a/mlibc/include/time.h
+++ b/mlibc/include/time.h
@@ -21,6 +21,7 @@
 #define __MES_TIME_H 1
 
 #if __GNUC__ && POSIX
+#undef __MES_TIME_H
 #include_next <time.h>
 #else // ! (__GNUC__ && POSIX)
 typedef int time_t;
diff --git a/mlibc/include/unistd.h b/mlibc/include/unistd.h
index fdb6808c..332d9363 100644
--- a/mlibc/include/unistd.h
+++ b/mlibc/include/unistd.h
@@ -24,6 +24,7 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #endif
+#undef __MES_UNISTD_H
 #include_next <unistd.h>
 
 #else // ! (__GNUC__ && POSIX)