diff --git a/src/libfetchers/git.cc b/src/libfetchers/git.cc
index f7e4894fc..cf255c001 100644
--- a/src/libfetchers/git.cc
+++ b/src/libfetchers/git.cc
@@ -883,7 +883,8 @@ struct GitInputScheme : InputScheme
 
     bool isLocked(const Input & input) const override
     {
-        return (bool) input.getRev();
+        auto rev = input.getRev();
+        return rev && rev != nullRev;
     }
 };