diff --git a/scripts/transparency_signing.py b/scripts/transparency_signing.py
index f587bf9e2..95dcd5d40 100644
--- a/scripts/transparency_signing.py
+++ b/scripts/transparency_signing.py
@@ -20,6 +20,7 @@ from scripts.transparency_core import failure
 
 REQUIRED_MINISIGN_VERSION = "minisign 0.12"
 MISSING_MINISIGN_MESSAGE = "transparency-minisign: minisign 0.12 is required; install it with: sudo dnf install minisign"
+TRUSTED_COMMENT_PREFIX = "trusted comment: "
 
 
 class TransparencySigner(Protocol):
@@ -78,6 +79,21 @@ def check_minisign_binary(minisign: str = "minisign") -> str:
     return version
 
 
+def _extract_trusted_comment(line: str, *, malformed_error: str, repair: str) -> str:
+    if not line.startswith(TRUSTED_COMMENT_PREFIX):
+        raise DriverError(
+            [
+                failure(
+                    malformed_error,
+                    expected=f"{TRUSTED_COMMENT_PREFIX}<trusted comment>",
+                    actual=line,
+                    repair=repair,
+                )
+            ]
+        )
+    return line[len(TRUSTED_COMMENT_PREFIX) :]
+
+
 @dataclass
 class LocalMinisignSigner:
     secret_key: Path
@@ -180,7 +196,6 @@ class LocalMinisignSigner:
             text=True,
             check=False,
         )
-        comment = result.stdout.strip()
         if result.returncode != 0:
             raise DriverError(
                 [
@@ -194,6 +209,7 @@ class LocalMinisignSigner:
                     )
                 ]
             )
+        comment = result.stdout.strip()
         if comment != expected_trusted_comment:
             raise DriverError(
                 [
@@ -219,7 +235,11 @@ class LocalMinisignSigner:
                     )
                 ]
             )
-        return lines[2]
+        return _extract_trusted_comment(
+            lines[2],
+            malformed_error="transparency minisign trusted comment line is malformed",
+            repair="re-sign the transparency object with minisign 0.12",
+        )
 
 
 @dataclass(frozen=True)
@@ -244,7 +264,7 @@ class FakeTransparencySigner:
                 (
                     "untrusted comment: fake transparency signature",
                     base64.b64encode(digest).decode("ascii"),
-                    trusted_comment,
+                    f"trusted comment: {trusted_comment}",
                     f"trusted comment signature: {hashlib.sha256(digest).hexdigest()}",
                     "",
                 )
@@ -271,7 +291,7 @@ class FakeTransparencySigner:
                     )
                 ]
             )
-        comment = lines[2]
+        comment = self.trusted_comment(signature_path)
         if comment != expected_trusted_comment:
             raise DriverError(
                 [
@@ -313,4 +333,8 @@ class FakeTransparencySigner:
                     )
                 ]
             )
-        return lines[2]
+        return _extract_trusted_comment(
+            lines[2],
+            malformed_error="fake transparency trusted comment line is malformed",
+            repair="re-sign the transparency object",
+        )
diff --git a/tests/test_transparency_signing.py b/tests/test_transparency_signing.py
index 831edbd4a..9a72dbf51 100644
--- a/tests/test_transparency_signing.py
+++ b/tests/test_transparency_signing.py
@@ -5,7 +5,7 @@ from pathlib import Path
 import pytest
 
 from scripts.release_candidate_driver import DriverError
-from scripts.transparency_signing import FakeTransparencySigner
+from scripts.transparency_signing import TRUSTED_COMMENT_PREFIX, FakeTransparencySigner
 
 
 def test_fake_signer_verifies_body_and_trusted_comment(tmp_path: Path) -> None:
@@ -39,7 +39,8 @@ def test_fake_signer_trusted_comment_is_line_three(tmp_path: Path) -> None:
     message.write_bytes(b'{"ok":1}\n')
     signer.sign_file(message, signature, trusted_comment=comment)
     lines = signature.read_text(encoding="utf-8").splitlines()
-    assert lines[2] == comment
+    assert len(lines) == 4
+    assert lines[2] == f"{TRUSTED_COMMENT_PREFIX}{comment}"
     assert signer.trusted_comment(signature) == comment
 
 
@@ -68,3 +69,26 @@ def test_fake_signer_rejects_trusted_comment_mismatch(tmp_path: Path) -> None:
     with pytest.raises(DriverError) as error:
         signer.verify_file(message, signature, expected_trusted_comment="two")
     assert error.value.failures[0].error == "fake transparency trusted comment mismatch"
+
+
+def test_fake_signer_rejects_missing_trusted_comment_prefix(tmp_path: Path) -> None:
+    signer = FakeTransparencySigner()
+    signature = tmp_path / "latest.json.minisig"
+    signature.write_text(
+        "\n".join(
+            (
+                "untrusted comment: fake transparency signature",
+                "ZmFrZQ==",
+                "raw trusted comment",
+                "trusted comment signature: fake",
+                "",
+            )
+        ),
+        encoding="utf-8",
+    )
+    with pytest.raises(DriverError) as error:
+        signer.trusted_comment(signature)
+    assert (
+        error.value.failures[0].error
+        == "fake transparency trusted comment line is malformed"
+    )