diff --git a/lang/rust/src/registry.sld b/lang/rust/src/registry.sld
index 77a657b..5275a93 100644
--- a/lang/rust/src/registry.sld
+++ b/lang/rust/src/registry.sld
@@ -127,7 +127,9 @@
        (create-directory repo #t)
        (let-values (((_ _ _) (process-wait (process-run "git" (list "init" "--bare" repo))))) #f))
 
-     (define-values (_ _ _) (process-wait (process-run "git" (list "-C" repo "fetch" "--write-fetch-head" url refspec))))
+     (define-values (_ commit-exists _) (process-wait (process-run "git" (list "-C" repo "cat-file" "-e" refspec))))
+     (unless commit-exists
+       (let-values (((_ _ _) (process-wait (process-run "git" (list "-C" repo "fetch" "--write-fetch-head" url refspec))))) #f))
      (define tree (read-git-tree repo (string-append refspec ":")))
      (define subdir (find-matching-cargo tree name))
      (unless subdir (error "could not find package in git repo" (list url refspec name)))