diff --git a/libc/include/sys/mman.h b/libc/include/sys/mman.h
index a3dc95c..9a2ec35 100644
--- a/libc/include/sys/mman.h
+++ b/libc/include/sys/mman.h
@@ -43,17 +43,12 @@
 #define MREMAP_MAYMOVE  1
 #define MREMAP_FIXED    2
 
-#define POSIX_MADV_NORMAL     MADV_NORMAL
-#define POSIX_MADV_RANDOM     MADV_RANDOM
-#define POSIX_MADV_SEQUENTIAL MADV_SEQUENTIAL
-#define POSIX_MADV_WILLNEED   MADV_WILLNEED
-#define POSIX_MADV_DONTNEED   MADV_DONTNEED
-
 #if defined(__USE_FILE_OFFSET64) && __ANDROID_API__ >= __ANDROID_API_L__
 void* mmap(void*, size_t, int, int, int, off_t) __RENAME(mmap64) __INTRODUCED_IN(21);
 #else
 void* mmap(void*, size_t, int, int, int, off_t);
 #endif
+
 void* mmap64(void*, size_t, int, int, int, off64_t) __INTRODUCED_IN(21);
 
 int munmap(void*, size_t);
@@ -63,12 +58,29 @@
 
 int mlockall(int) __INTRODUCED_IN(17);
 int munlockall(void) __INTRODUCED_IN(17);
+
 int mlock(const void*, size_t);
 int munlock(const void*, size_t);
 
 int mincore(void*, size_t, unsigned char*);
 
 int madvise(void*, size_t, int);
+
+#if __ANDROID_API__ >= __ANDROID_API_M__
+/*
+ * Some third-party code uses the existence of POSIX_MADV_NORMAL to detect the
+ * availability of posix_madvise. This is not correct, since having up-to-date
+ * UAPI headers says nothing about the C library, but for the time being we
+ * don't want to harm adoption to the unified headers.
+ *
+ * https://github.com/android-ndk/ndk/issues/395
+ */
+#define POSIX_MADV_NORMAL     MADV_NORMAL
+#define POSIX_MADV_RANDOM     MADV_RANDOM
+#define POSIX_MADV_SEQUENTIAL MADV_SEQUENTIAL
+#define POSIX_MADV_WILLNEED   MADV_WILLNEED
+#define POSIX_MADV_DONTNEED   MADV_DONTNEED
+#endif
 int posix_madvise(void*, size_t, int) __INTRODUCED_IN(23);
 
 __END_DECLS