diff --git a/libc/include/unistd.h b/libc/include/unistd.h
index 91b0d8d..29758f5 100644
--- a/libc/include/unistd.h
+++ b/libc/include/unistd.h
@@ -159,7 +159,7 @@
 extern int pause(void);
 extern unsigned int alarm(unsigned int);
 extern unsigned int sleep(unsigned int);
-extern int usleep(unsigned long);
+extern int usleep(useconds_t);
 
 extern int gethostname(char *, size_t);