diff --git a/crosscompilemakefile.mak b/crosscompilemakefile.mak
index 6ba47887..a1ce9423 100644
--- a/crosscompilemakefile.mak
+++ b/crosscompilemakefile.mak
@@ -21,7 +21,7 @@ LIBMAXSIROOT=$(OSROOT)/libmaxsi
 LIBC=$(LIBMAXSIROOT)/start.o $(LIBMAXSIROOT)/libc.a
 LIBS=$(LIBC)
 
-CPPFLAGS=$(CPUDEFINES)
+CPPFLAGS=$(CPUDEFINES) -U_GNU_SOURCE
 FLAGS=-nostdinc -nostdlib -fno-builtin -nostartfiles -nodefaultlibs
 INCLUDES=-I $(LIBMAXSIROOT)/c/h/ -I $(OSROOT)/
 
diff --git a/libmaxsi/Makefile b/libmaxsi/Makefile
index 8f1ab344..7c1eabca 100644
--- a/libmaxsi/Makefile
+++ b/libmaxsi/Makefile
@@ -20,7 +20,7 @@ ifeq ($(CPU),x64)
     LIBMAXSI_NO_SHARED=1 # This doesn't work yet
 endif
 
-DEFINES=-DLIBMAXSI_LIBRARY -DSORTIX $(CPUDEFINES)
+DEFINES=-DLIBMAXSI_LIBRARY -DSORTIX -U_GNU_SOURCE $(CPUDEFINES)
 FLAGSRELEASE=-O2
 FLAGSDEBUG=-O2
 FLAGS=$(CPUFLAGS) -std=gnu++0x -Wall -Wextra -nostdlib -fno-builtin -nostartfiles -nodefaultlibs -fno-exceptions -fno-stack-protector -nostdinc $(FLAGSRELEASE) $(DEFINES)
diff --git a/libmaxsi/c/hsrc/dirent.h b/libmaxsi/c/hsrc/dirent.h
index 12acf7f2..8945eff2 100644
--- a/libmaxsi/c/hsrc/dirent.h
+++ b/libmaxsi/c/hsrc/dirent.h
@@ -43,7 +43,7 @@ DIR* opendir(const char* path);
 struct dirent* readdir(DIR* dir);
 void rewinddir(DIR* dir);
 
-#ifdef SORTIX_EXTENSIONS
+#if defined(_SORTIX_SOURCE)
 void dregister(DIR* dir);
 void dunregister(DIR* dir);
 DIR* dnewdir(void);
diff --git a/libmaxsi/c/hsrc/fcntl.h b/libmaxsi/c/hsrc/fcntl.h
index d100fd28..418cd145 100644
--- a/libmaxsi/c/hsrc/fcntl.h
+++ b/libmaxsi/c/hsrc/fcntl.h
@@ -86,7 +86,7 @@ typedef struct _flock flock;
 
 /* TODO: These are not implemented in libmaxsi/sortix yet. */
 int open(const char* path, int oflag, ...);
-#ifndef SORTIX_UNIMPLEMENTED
+#if defined(__SORTIX_SHOW_UNIMPLEMENTED)
 int creat(const char* path, mode_t mode);
 int fcntl(int fd, int cmd, ...);
 int openat(int fd, const char* path, int oflag, ...);
diff --git a/libmaxsi/c/hsrc/features.h b/libmaxsi/c/hsrc/features.h
index 21e2d441..a7e359fe 100644
--- a/libmaxsi/c/hsrc/features.h
+++ b/libmaxsi/c/hsrc/features.h
@@ -34,8 +34,52 @@
 	#define __END_DECLS
 #endif
 
+/* By default, assume the source is compiled using the native API. */
+#if !defined(_SORTIX_SOURCE) && \
+    !defined(_POSIX_SOURCE) && !defined(_POSIX_C_SOURCE) && \
+    !defined(_BSD_SOURCE) && \
+    !defined(_SVID_SOURCE) && \
+    !defined(_XOPEN_SOURCE) && !defined(_XOPEN_SOURCE_EXTENDED) && \
+    !defined(_GNU_SOURCE) && \
+    true
+	#define _SORTIX_SOURCE 1
+#endif
+
+#ifdef _SORTIX_SOURCE
+	#warning _SORTIX_SOURCE
+#endif
+
+#ifdef _POSIX_SOURCE
+	#warning _POSIX_SOURCE
+#endif
+
+#ifdef _POSIX_C_SOURCE
+	#warning _POSIX_C_SOURCE
+#endif
+
+#ifdef _BSD_SOURCE
+	#warning _BSD_SOURCE
+#endif
+
+#ifdef _SVID_SOURCE
+	#warning _SVID_SOURCE
+#endif
+
+#ifdef _XOPEN_SOURCE
+	#warning _XOPEN_SOURCE
+#endif
+
+#ifdef _XOPEN_SOURCE_EXTENDED
+	#warning XOPEN_SOURCE_EXTENDED
+#endif
+
+#ifdef _GNU_SOURCE
+	#warning _GNU_SOURCE
+#endif
+
 #define restrict
 
+/* TODO: Improve these declarations, perhaps like they are in glibc. */
 #define __POSIX_NO_OBSOLETE
 
 #ifdef __POSIX_NO_OBSOLETE
@@ -44,13 +88,8 @@
 	#define __POSIX_OBSOLETE 200112L
 #endif
 
-/* Whether sortix-specific extensions to the C library are available. */
-#ifndef SORTIX_NO_EXTENSIONS
-#define SORTIX_EXTENSIONS
-#endif
-
 /* Don't provide things from standard headers that is not implemented. */
-#define SORTIX_UNIMPLEMENTED
+/*#define __SORTIX_SHOW_UNIMPLEMENTED*/
 
 #include <sortix/bits.h>
 
diff --git a/libmaxsi/c/hsrc/stdio.h b/libmaxsi/c/hsrc/stdio.h
index e6179e60..cd783b89 100644
--- a/libmaxsi/c/hsrc/stdio.h
+++ b/libmaxsi/c/hsrc/stdio.h
@@ -108,7 +108,7 @@ extern int vsnprintf(char* restrict, size_t, const char* restrict, va_list);
 extern int vsprintf(char* restrict s, const char* restrict format, va_list ap);
 
 /* TODO: These are not implemented in libmaxsi/sortix yet. */
-#ifndef SORTIX_UNIMPLEMENTED
+#if defined(__SORTIX_SHOW_UNIMPLEMENTED)
 extern char* ctermid(char* s);
 extern char* fgets(char* restrict s, int n, FILE* restrict stream);
 extern FILE *fmemopen(void* restrict buf, size_t size, const char* restrict mode);
@@ -151,7 +151,7 @@ extern char* tempnam(const char* dir, const char* pfx);
 #endif
 #endif
 
-#ifdef SORTIX_EXTENSIONS
+#if defined(_SORTIX_SOURCE)
 void fregister(FILE* fp);
 void funregister(FILE* fp);
 FILE* fnewfile(void);
diff --git a/libmaxsi/c/hsrc/stdlib.h b/libmaxsi/c/hsrc/stdlib.h
index a65bcac9..0c972699 100644
--- a/libmaxsi/c/hsrc/stdlib.h
+++ b/libmaxsi/c/hsrc/stdlib.h
@@ -58,7 +58,7 @@ unsigned long long strtoull(const char* restrict, char** restrict, int);
 long long strtoll(const char* restrict, char** restrict, int);
 
 /* TODO: These are not implemented in libmaxsi/sortix yet. */
-#ifndef SORTIX_UNIMPLEMENTED
+#if defined(__SORTIX_SHOW_UNIMPLEMENTED)
 long a64l(const char* s);
 void abort(void);
 int abs(int value);
diff --git a/libmaxsi/c/hsrc/string.h b/libmaxsi/c/hsrc/string.h
index a5121939..9fe71b94 100644
--- a/libmaxsi/c/hsrc/string.h
+++ b/libmaxsi/c/hsrc/string.h
@@ -53,7 +53,7 @@ char* strtok(char* restrict, const char* restrict);
 char* strtok_r(char* restrict, const char* restrict, char** restrict);
 
 /* TODO: These are not implemented in libmaxsi/sortix yet. */
-#ifndef SORTIX_UNIMPLEMENTED
+#if defined(__SORTIX_SHOW_UNIMPLEMENTED)
 void* memccpy(void* restrict, const void* restrict, int, size_t);
 void* memmove(void*, const void*, size_t);
 char* stpncpy(char* restrict, const char* restrict, size_t);
@@ -72,7 +72,7 @@ size_t strxfrm(char* restrict, const char* restrict, size_t);
 size_t strxfrm_l(char* restrict, const char* restrict, size_t, locale_t);
 #endif
 
-#ifdef SORTIX_EXTENSIONS
+#if defined(_SORTIX_SOURCE) || defined(_GNU_SOURCE)
 char* strchrnul(const char* str, int c);
 #endif
 
diff --git a/libmaxsi/c/hsrc/sys/wait.h b/libmaxsi/c/hsrc/sys/wait.h
index 232ccd10..6278f9ae 100644
--- a/libmaxsi/c/hsrc/sys/wait.h
+++ b/libmaxsi/c/hsrc/sys/wait.h
@@ -34,7 +34,7 @@ __BEGIN_DECLS
 @include(pid_t.h)
 
 /* TODO: These are not implemented in libmaxsi/sortix yet. */
-#ifndef SORTIX_UNIMPLEMENTED
+#if defined(__SORTIX_SHOW_UNIMPLEMENTED)
 int waitid(idtype_t, id_t, siginfo_t*, int);
 #endif
 
diff --git a/libmaxsi/c/hsrc/unistd.h b/libmaxsi/c/hsrc/unistd.h
index 9cc326b3..a6302b73 100644
--- a/libmaxsi/c/hsrc/unistd.h
+++ b/libmaxsi/c/hsrc/unistd.h
@@ -74,12 +74,12 @@ __BEGIN_DECLS
 @include(off_t.h)
 @include(pid_t.h)
 @include(useconds_t.h)
-#ifdef SORTIX_EXTENSIONS
+#if defined(_SORTIX_SOURCE)
 @include(intn_t.h)
 #endif
 
 /* TODO: These are not implemented in libmaxsi/sortix yet. */
-#ifndef SORTIX_UNIMPLEMENTED
+#if defined(__SORTIX_SHOW_UNIMPLEMENTED)
 int access(const char*, int);
 unsigned alarm(unsigned);
 int chown(const char*, uid_t, gid_t);
@@ -169,13 +169,13 @@ ssize_t read(int, void*, size_t);
 int rmdir(const char*);
 unsigned sleep(unsigned);
 int truncate(const char*, off_t);
-#if __POSIX_OBSOLETE <= 200112 || defined(SORTIX_EXTENSIONS)
+#if __POSIX_OBSOLETE <= 200112 || defined(_SORTIX_SOURCE)
 int usleep(useconds_t useconds);
 #endif
 int unlink(const char*);
 ssize_t write(int, const void*, size_t);
 
-#ifdef SORTIX_EXTENSIONS
+#if defined(_SORTIX_SOURCE)
 size_t getpagesize(void);
 int memstat(size_t* memused, size_t* memtotal);
 int uptime(uintmax_t* usecssinceboot);
diff --git a/libmaxsi/c/hsrc/wchar.h b/libmaxsi/c/hsrc/wchar.h
index 3c44e7d2..476f76e5 100644
--- a/libmaxsi/c/hsrc/wchar.h
+++ b/libmaxsi/c/hsrc/wchar.h
@@ -61,7 +61,7 @@ __BEGIN_DECLS
 struct tm;
 
 /* TODO: These are not implemented in libmaxsi/sortix yet. */
-#ifndef SORTIX_UNIMPLEMENTED
+#if defined(__SORTIX_SHOW_UNIMPLEMENTED)
 double wcstod(const wchar_t* restrict, wchar_t** restrict);
 FILE* open_wmemstream(wchar_t** bufp, size_t* sizep);
 float wcstof(const wchar_t* restrict, wchar_t** restrict);
diff --git a/libmaxsi/c/hsrc/wctype.h b/libmaxsi/c/hsrc/wctype.h
index 92cd44d6..83ce3319 100644
--- a/libmaxsi/c/hsrc/wctype.h
+++ b/libmaxsi/c/hsrc/wctype.h
@@ -35,7 +35,7 @@ __BEGIN_DECLS
 @include(WEOF.h)
 
 /* TODO: These are not implemented in libmaxsi/sortix yet. */
-#ifndef SORTIX_UNIMPLEMENTED
+#if defined(__SORTIX_SHOW_UNIMPLEMENTED)
 int iswalnum(wint_t);
 int iswalnum_l(wint_t, locale_t);
 int iswalpha(wint_t);
diff --git a/sortix/Makefile b/sortix/Makefile
index f12b5fdc..2094864c 100644
--- a/sortix/Makefile
+++ b/sortix/Makefile
@@ -44,7 +44,7 @@ endif
 
 DIRS=. x64 x86 x86-family fs kb kb/layout
 
-DEFINES:=-DSORTIX_KERNEL $(CPUDEFINES)
+DEFINES:=-DSORTIX_KERNEL -U_GNU_SOURCE $(CPUDEFINES)
 ifeq ($(JSSORTIX),1)
     DEFINES:=$(DEFINES) -DPLATFORM_SERIAL -DJSSORTIX
     BUILDID:=$(BUILDID)-js