diff --git a/cache.h b/cache.h
index b829410f6d..02e38d1a91 100644
--- a/cache.h
+++ b/cache.h
@@ -747,7 +747,14 @@ extern int grafts_replace_parents;
 #define GIT_REPO_VERSION_READ 1
 extern int repository_format_version;
 extern int repository_format_precious_objects;
-extern int check_repository_format(void);
+
+/*
+ * Check the repository format version in the path found in get_git_dir(),
+ * and die if it is a version we don't understand. Generally one would
+ * set_git_dir() before calling this, and use it only for "are we in a valid
+ * repo?".
+ */
+extern void check_repository_format(void);
 
 #define MTIME_CHANGED	0x0001
 #define CTIME_CHANGED	0x0002
diff --git a/setup.c b/setup.c
index de1a2a7ea5..b2f2e690e4 100644
--- a/setup.c
+++ b/setup.c
@@ -982,9 +982,9 @@ int check_repository_format_version(const char *var, const char *value, void *cb
 	return 0;
 }
 
-int check_repository_format(void)
+void check_repository_format(void)
 {
-	return check_repository_format_gently(get_git_dir(), NULL);
+	check_repository_format_gently(get_git_dir(), NULL);
 }
 
 /*