diff --git a/src/HW/SCREEN/SCRNEMDV.h b/src/HW/SCREEN/SCRNEMDV.h
index 7f7e36e..3b493a1 100644
--- a/src/HW/SCREEN/SCRNEMDV.h
+++ b/src/HW/SCREEN/SCRNEMDV.h
@@ -32,8 +32,8 @@ extern uint32_t vMacScreenBitWidth;
 extern uint32_t vMacScreenByteWidth;
 extern uint32_t vMacScreenMonoNumBytes;
 extern uint32_t vMacScreenMonoByteWidth;
-bool UseLargeScreenHack;
-char *ScreenColorBlack;
-char *ScreenColorWhite;
+extern bool UseLargeScreenHack;
+extern char *ScreenColorBlack;
+extern char *ScreenColorWhite;
 
 #endif