diff --git a/libc/stdio/fpurge.c b/libc/stdio/fpurge.c
index fa0213a..e04c4fe 100644
--- a/libc/stdio/fpurge.c
+++ b/libc/stdio/fpurge.c
@@ -43,7 +43,9 @@
 int
 fpurge(FILE *fp)
 {
+	FLOCKFILE(fp);
 	if (!fp->_flags) {
+		FUNLOCKFILE(fp);
 		errno = EBADF;
 		return(EOF);
 	}
@@ -54,5 +56,6 @@
 	fp->_p = fp->_bf._base;
 	fp->_r = 0;
 	fp->_w = fp->_flags & (__SLBF|__SNBF) ? 0 : fp->_bf._size;
+	FUNLOCKFILE(fp);
 	return (0);
 }