diff --git a/libc/SYSCALLS.TXT b/libc/SYSCALLS.TXT
index d263508..ec34828 100644
--- a/libc/SYSCALLS.TXT
+++ b/libc/SYSCALLS.TXT
@@ -113,7 +113,7 @@
 int         msync(const void*, size_t, int)    all
 int         mprotect(const void*, size_t, int)  all
 int         madvise(void*, size_t, int)  all
-int         process_madvise(int, const struct iovec*, size_t, int, unsigned int)     all
+ssize_t     process_madvise(int, const struct iovec*, size_t, int, unsigned int)     all
 int mlock(const void* addr, size_t len)    all
 int mlock2(const void* addr, size_t len, int flags)    all
 int         munlock(const void* addr, size_t len)   all
diff --git a/libc/include/sys/mman.h b/libc/include/sys/mman.h
index 3b44dab..6ef0c12 100644
--- a/libc/include/sys/mman.h
+++ b/libc/include/sys/mman.h
@@ -167,9 +167,9 @@
  * works just like madvise(2) but applies to the process specified by the given
  * PID file descriptor.
  *
- * Returns 0 on success, and returns -1 and sets `errno` on failure.
+ * Returns the number of bytes advised on success, and returns -1 and sets `errno` on failure.
  */
-int process_madvise(int __pid_fd, const struct iovec* __iov, size_t __count, int __advice, unsigned int __flags);
+ssize_t process_madvise(int __pid_fd, const struct iovec* __iov, size_t __count, int __advice, unsigned __flags);
 
 #if defined(__USE_GNU)