diff --git a/guix/build/store-copy.scm b/guix/build/store-copy.scm
index 549aa4f28b..ad551bca98 100644
--- a/guix/build/store-copy.scm
+++ b/guix/build/store-copy.scm
@@ -35,6 +35,7 @@
 
             read-reference-graph
 
+            file-size
             closure-size
             populate-store))