diff --git a/klibc/klibc/include/unistd.h b/klibc/klibc/include/unistd.h
index a9b434c16b..3c51c497a7 100644
--- a/klibc/klibc/include/unistd.h
+++ b/klibc/klibc/include/unistd.h
@@ -103,6 +103,8 @@ __extern int optind, opterr, optopt;
 
 __extern int isatty(int);
 
+__extern int ftruncate(int, off_t);
+
 /* Standard file descriptor numbers. */
 #define STDIN_FILENO	0
 #define STDOUT_FILENO	1