diff --git a/pkgs/build-support/fetchgit/default.nix b/pkgs/build-support/fetchgit/default.nix
index 5cf447e37a0d..bbf756fde2f3 100644
--- a/pkgs/build-support/fetchgit/default.nix
+++ b/pkgs/build-support/fetchgit/default.nix
@@ -177,7 +177,8 @@ lib.makeOverridable (
           sparseCheckoutText =
             # Changed to throw on 2023-06-04
             assert (
-              lib.assertMsg (lib.isList finalAttrs.sparseCheckout) "Please provide directories/patterns for sparse checkout as a list of strings. Passing a (multi-line) string is not supported any more."
+              lib.isList finalAttrs.sparseCheckout
+              || throw "Please provide directories/patterns for sparse checkout as a list of strings. Passing a (multi-line) string is not supported any more."
             );
             assert finalAttrs.nonConeMode -> (finalAttrs.sparseCheckout != [ ]);
             # git-sparse-checkout(1) says: