diff --git a/process.go b/process.go
index c2b9f316..bcffaba9 100644
--- a/process.go
+++ b/process.go
@@ -3,6 +3,7 @@ package main
 /*
 #cgo pkg-config: vips
 #cgo LDFLAGS: -s -w
+#cgo CFLAGS: -O3
 #include "vips.h"
 */
 import "C"