diff --git a/libc/include/sys/cdefs.h b/libc/include/sys/cdefs.h
index 9c662ba..9541520 100644
--- a/libc/include/sys/cdefs.h
+++ b/libc/include/sys/cdefs.h
@@ -111,39 +111,6 @@
 #define __unused __attribute__((__unused__))
 #define __used __attribute__((__used__))
 
-/*
- * _Nonnull is similar to the nonnull attribute in that it will instruct
- * compilers to warn the user if it can prove that a null argument is being
- * passed. Unlike the nonnull attribute, this annotation indicated that a value
- * *should not* be null, not that it *cannot* be null, or even that the behavior
- * is undefined. The important distinction is that the optimizer will perform
- * surprising optimizations like the following:
- *
- *     void foo(void*) __attribute__(nonnull, 1);
- *
- *     int bar(int* p) {
- *       foo(p);
- *
- *       // The following null check will be elided because nonnull attribute
- *       // means that, since we call foo with p, p can be assumed to not be
- *       // null. Thus this will crash if we are called with a null pointer.
- *       if (p != NULL) {
- *         return *p;
- *       }
- *       return 0;
- *     }
- *
- *     int main() {
- *       return bar(NULL);
- *     }
- *
- * http://clang.llvm.org/docs/AttributeReference.html#nonnull
- */
-#if !(defined(__clang__) && __has_feature(nullability))
-#define _Nonnull
-#define _Nullable
-#endif
-
 #define __printflike(x, y) __attribute__((__format__(printf, x, y)))
 #define __scanflike(x, y) __attribute__((__format__(scanf, x, y)))
 
diff --git a/libc/include/sys/signalfd.h b/libc/include/sys/signalfd.h
index 79f9490..1e4d464 100644
--- a/libc/include/sys/signalfd.h
+++ b/libc/include/sys/signalfd.h
@@ -36,7 +36,7 @@
 
 __BEGIN_DECLS
 
-int signalfd(int fd, const sigset_t* _Nonnull mask, int flags) __INTRODUCED_IN(18);
+int signalfd(int fd, const sigset_t* mask, int flags) __INTRODUCED_IN(18);
 
 __END_DECLS
 
diff --git a/libc/include/sys/statvfs.h b/libc/include/sys/statvfs.h
index 5df4160..0f421a4 100644
--- a/libc/include/sys/statvfs.h
+++ b/libc/include/sys/statvfs.h
@@ -59,10 +59,10 @@
 #define ST_NODIRATIME  0x0800
 #define ST_RELATIME    0x1000
 
-int statvfs(const char* _Nonnull, struct statvfs* _Nonnull) __INTRODUCED_IN(19);
-int statvfs64(const char* _Nonnull, struct statvfs64* _Nonnull) __INTRODUCED_IN(21);
-int fstatvfs(int, struct statvfs* _Nonnull) __INTRODUCED_IN(19);
-int fstatvfs64(int, struct statvfs64* _Nonnull) __INTRODUCED_IN(21);
+int statvfs(const char*, struct statvfs*) __INTRODUCED_IN(19);
+int statvfs64(const char*, struct statvfs64*) __INTRODUCED_IN(21);
+int fstatvfs(int, struct statvfs*) __INTRODUCED_IN(19);
+int fstatvfs64(int, struct statvfs64*) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/sys/swap.h b/libc/include/sys/swap.h
index 3444736..e79af97 100644
--- a/libc/include/sys/swap.h
+++ b/libc/include/sys/swap.h
@@ -38,8 +38,8 @@
 #define SWAP_FLAG_PRIO_MASK 0x7fff
 #define SWAP_FLAG_PRIO_SHIFT 0
 
-int swapon(const char* _Nonnull, int) __INTRODUCED_IN(19);
-int swapoff(const char* _Nonnull) __INTRODUCED_IN(19);
+int swapon(const char*, int) __INTRODUCED_IN(19);
+int swapoff(const char*) __INTRODUCED_IN(19);
 
 __END_DECLS
 
diff --git a/libc/include/sys/vfs.h b/libc/include/sys/vfs.h
index 1231eb1..3078683 100644
--- a/libc/include/sys/vfs.h
+++ b/libc/include/sys/vfs.h
@@ -137,10 +137,10 @@
 #define XENIX_SUPER_MAGIC     0x012FF7B4
 #define XFS_SUPER_MAGIC       0x58465342
 
-int statfs(const char* _Nonnull, struct statfs* _Nonnull);
-int statfs64(const char* _Nonnull, struct statfs64* _Nonnull) __INTRODUCED_IN(21);
-int fstatfs(int, struct statfs* _Nonnull);
-int fstatfs64(int, struct statfs64* _Nonnull) __INTRODUCED_IN(21);
+int statfs(const char*, struct statfs*);
+int statfs64(const char*, struct statfs64*) __INTRODUCED_IN(21);
+int fstatfs(int, struct statfs*);
+int fstatfs64(int, struct statfs64*) __INTRODUCED_IN(21);
 
 __END_DECLS