diff --git a/tools/version-guard/check.ts b/tools/version-guard/check.ts
index bf5bdf0..a6a84c3 100644
--- a/tools/version-guard/check.ts
+++ b/tools/version-guard/check.ts
@@ -698,7 +698,18 @@ export async function cutGoldenChanges(
   lastTag: string,
   sha: string,
 ): Promise<GoldenChange[]> {
-  await fx.run("git", ["fetch", "origin", `refs/tags/${lastTag}`, "--depth=1"]);
+  // The full-refspec form is load-bearing: without a DESTINATION
+  // (`:refs/tags/…`) the fetch drops the objects into FETCH_HEAD but
+  // creates no local ref, so the tag NAME stays unresolvable and the diff
+  // below fails with "bad revision" (the v0.5.0 cut, first dispatch). The
+  // PR-base fetch this mirrors gets away with a bare source because a raw
+  // sha resolves from the object store alone; a tag name needs a ref.
+  await fx.run("git", [
+    "fetch",
+    "origin",
+    `+refs/tags/${lastTag}:refs/tags/${lastTag}`,
+    "--depth=1",
+  ]);
   let diff = await fx.run("git", [
     "diff",
     "--name-status",
diff --git a/tools/version-guard/check_test.ts b/tools/version-guard/check_test.ts
index c5af6c2..6587f37 100644
--- a/tools/version-guard/check_test.ts
+++ b/tools/version-guard/check_test.ts
@@ -625,7 +625,7 @@ Deno.test("cut: end to end — window scan, guards, and the notes fragment", asy
       }),
     },
     git: {
-      "fetch origin refs/tags/v0.4.0 --depth=1": {},
+      "fetch origin +refs/tags/v0.4.0:refs/tags/v0.4.0 --depth=1": {},
       "diff --name-status v0.4.0..cut12345 -- runtime/tests/conventions/golden/":
         { stdout: "" },
     },
@@ -797,7 +797,7 @@ function cutFake(over: {
       }),
     },
     git: {
-      "fetch origin refs/tags/v0.4.0 --depth=1": {},
+      "fetch origin +refs/tags/v0.4.0:refs/tags/v0.4.0 --depth=1": {},
       "diff --name-status v0.4.0..cut12345 -- runtime/tests/conventions/golden/":
         { stdout: over.goldenDiff ?? "" },
     },