diff --git a/redo/uitask_unix.go b/redo/uitask_unix.go
index b75a94d..8604dd2 100644
--- a/redo/uitask_unix.go
+++ b/redo/uitask_unix.go
@@ -10,6 +10,7 @@ import (
 )
 
 // #cgo pkg-config: gtk+-3.0
+// #cgo CFLAGS: --std=c99
 // #include "gtk_unix.h"
 // extern gboolean doissue(gpointer data);
 import "C"
diff --git a/redo/uitask_windows.go b/redo/uitask_windows.go
index 288b33f..54b29cb 100644
--- a/redo/uitask_windows.go
+++ b/redo/uitask_windows.go
@@ -8,6 +8,7 @@ import (
 	"unsafe"
 )
 
+// #cgo CFLAGS: --std=c99
 // #cgo LDFLAGS: -luser32 -lkernel32 -lgdi32 -luxtheme -lmsimg32
 // #include "winapi_windows.h"
 import "C"