https://bugs.gentoo.org/707770

--- a/src/mon-blows.h
+++ b/src/mon-blows.h
@@ -41,7 +41,7 @@ struct blow_method {
 	struct blow_method *next;
 };
 
-struct blow_method *blow_methods;
+extern struct blow_method *blow_methods;
 
 /**
  * Storage for context information for effect handlers called in
@@ -83,7 +83,7 @@ struct blow_effect {
 	struct blow_effect *next;
 };
 
-struct blow_effect *blow_effects;
+extern struct blow_effect *blow_effects;
 
 /* Functions */
 int blow_index(const char *name);
