diff --git a/libc/include/fcntl.h b/libc/include/fcntl.h
index 779a089..cd68154 100644
--- a/libc/include/fcntl.h
+++ b/libc/include/fcntl.h
@@ -37,6 +37,20 @@
 
 __BEGIN_DECLS
 
+#ifdef __LP64__
+/* LP64 kernels don't have flock64 because their flock is 64-bit. */
+struct flock64 {
+  short l_type;
+  short l_whence;
+  off64_t l_start;
+  off64_t l_len;
+  pid_t l_pid;
+};
+#define F_GETLK64  F_GETLK
+#define F_SETLK64  F_SETLK
+#define F_SETLKW64 F_SETLKW
+#endif
+
 #ifndef O_ASYNC
 #define O_ASYNC  FASYNC
 #endif