diff --git a/src/gui.h b/src/gui.h
--- a/src/gui.h
+++ b/src/gui.h
@@ -74,5 +74,4 @@ void ShowBuildIndustryWindow();
 void ShowFoundTownWindow();
 void ShowMusicWindow();
 
-
 #endif /* GUI_H */
diff --git a/src/transparency.h b/src/transparency.h
--- a/src/transparency.h
+++ b/src/transparency.h
@@ -38,6 +38,7 @@ typedef uint TransparencyOptionBits; ///
 extern TransparencyOptionBits _transparency_opt;
 extern TransparencyOptionBits _transparency_lock;
 extern TransparencyOptionBits _invisibility_opt;
+extern byte _display_opt; ///< What do we want to draw/do?
 
 /**
  * Check if the transparency option bit is set
diff --git a/src/transparency_gui.cpp b/src/transparency_gui.cpp
--- a/src/transparency_gui.cpp
+++ b/src/transparency_gui.cpp
@@ -20,6 +20,7 @@
 TransparencyOptionBits _transparency_opt;
 TransparencyOptionBits _transparency_lock;
 TransparencyOptionBits _invisibility_opt;
+byte _display_opt;
 
 /** Widget numbers of the transparency window. */
 enum TransparencyToolbarWidgets {
diff --git a/src/variables.h b/src/variables.h
--- a/src/variables.h
+++ b/src/variables.h
@@ -19,8 +19,6 @@
 /* Amount of game ticks */
 VARDEF uint16 _tick_counter;
 
-VARDEF byte _display_opt;
-
 /* IN/OUT parameters to commands */
 VARDEF bool _generating_world;