diff --git a/include/tr/class.h b/include/tr/class.h
index 98487eb..e76126c 100644
--- a/include/tr/class.h
+++ b/include/tr/class.h
@@ -61,7 +61,7 @@
  * that are needed to create a new class.
  */
 #define TR_CLASS(name)                      \
-	struct TR_class c_##name;               \
+	extern struct TR_class c_##name;        \
 	struct c_##name;                        \
 	typedef struct c_##name * name;         \
 	extern struct TR_class * const _##name; \