diff --git a/futility/futility.h b/futility/futility.h
index c815003..6a593fb 100644
--- a/futility/futility.h
+++ b/futility/futility.h
@@ -40,7 +40,7 @@
 };
 
 /* What's our preferred API & data format? */
-enum vboot_version vboot_version;
+extern enum vboot_version vboot_version;
 
 /* Here's a structure to define the commands that futility implements. */
 struct futil_cmd_t {