diff --git a/ueberzug/X/Xshm.h b/ueberzug/X/Xshm.h
index 9368233..ab61b4d 100644
--- a/ueberzug/X/Xshm.h
+++ b/ueberzug/X/Xshm.h
@@ -3,5 +3,5 @@
 #include "python.h"
 
 
-PyTypeObject ImageType;
+extern PyTypeObject ImageType;
 #endif
diff --git a/ueberzug/X/display.h b/ueberzug/X/display.h
index d7fcdc4..8492607 100644
--- a/ueberzug/X/display.h
+++ b/ueberzug/X/display.h
@@ -24,6 +24,6 @@ typedef struct {
     Atom wm_locale_name;
     Atom wm_normal_hints;
 } DisplayObject;
-PyTypeObject DisplayType;
+extern PyTypeObject DisplayType;
 
 #endif
diff --git a/ueberzug/X/window.h b/ueberzug/X/window.h
index 7380618..ac59417 100644
--- a/ueberzug/X/window.h
+++ b/ueberzug/X/window.h
@@ -3,5 +3,5 @@
 #include "python.h"
 
 
-PyTypeObject WindowType;
+extern PyTypeObject WindowType;
 #endif