diff --git a/cli/__tests__/git-readonly.test.mjs b/cli/__tests__/git-readonly.test.mjs
index fe62bd76c4..9c464c56c6 100644
--- a/cli/__tests__/git-readonly.test.mjs
+++ b/cli/__tests__/git-readonly.test.mjs
@@ -429,6 +429,36 @@ describe('read-only git runs no gpg and no textconv', () => {
     expect(ran('gpg')).toBe(false);
   });
 
+  test('a %G placeholder behind a +, - or space modifier runs gpg (control), and is refused', async () => {
+    for (const format of ['%+G?', '%-GG', '% GS']) {
+      await cfgGit(['log', `--format=${format}`, '-1', signed]);
+      expect(ran('gpg')).toBe(true);
+    }
+    for (const arg of ['--format=%+G?', '--pretty=format:%-GK', '--pretty=tformat:%h% GF', '--format=%<(8)%+GP', '--format=%-GT']) {
+      expect((await run('log', [arg, '-1', signed])).text).toMatch(/%G placeholder runs gpg/);
+    }
+    expect(ran('gpg')).toBe(false);
+    const modified = await run('log', ['--format=%h%+s', '-1', signed]);
+    expect(modified.ok).toBe(true);
+    expect(modified.text).toContain('\nunsigned');
+  });
+
+  // git 2.54 rejects every abbreviation of --pretty and --format, and a bare
+  // --format, so none of these has a control: the check holds without that.
+  test('an abbreviation is checked like the full name, and --format never takes the next argument', () => {
+    expect(refusal({ subcommand: 'log', args: ['--form=%G?'] })).toMatch(/%G placeholder runs gpg/);
+    expect(refusal({ subcommand: 'show', args: ['--pret=format:%+GS'] })).toMatch(/%G placeholder runs gpg/);
+    expect(refusal({ subcommand: 'log', args: ['--forma=sig'] })).toMatch(/name a built-in format/);
+    for (const option of ['--format', '--form', '--for']) {
+      expect(refusal({ subcommand: 'log', args: [option, '%G?'] })).toMatch(/give the format in the same argument/);
+    }
+    for (const args of [['--form=%h'], ['--pret=oneline'], ['--pretty'], ['--pretty', '-n1']]) {
+      expect(readonlyGitArgv({ subcommand: 'log', args, root: repo }).ok).toBe(true);
+    }
+    // blame reads --pr as its own --progress.
+    expect(readonlyGitArgv({ subcommand: 'blame', args: ['--pr', 'tracked.txt'], root: repo }).ok).toBe(true);
+  });
+
   test('log.showSignature in the repository config runs gpg (control); the guarded log and show do not', async () => {
     await cfgGit(['config', 'log.showSignature', 'true']);
     try {
diff --git a/cli/src/lib/git-readonly.js b/cli/src/lib/git-readonly.js
index 6cdc9825e4..509dd19808 100644
--- a/cli/src/lib/git-readonly.js
+++ b/cli/src/lib/git-readonly.js
@@ -127,16 +127,28 @@ const TOP_LEVEL = Object.freeze([
 ]);
 
 // A %G placeholder (%G?, %GG, %GS, %GK, %GF, %GP, %GT) runs gpg on each signed
-// commit. A value with no %, no format: and no tformat: is looked up by
-// prefix among the built-in formats and the repository's `pretty.<name>`
-// aliases, and an alias can hold one, so only a built-in name is taken.
-const FORMAT_ARGUMENT = /^--(?:pretty|format)=([\s\S]*)$/;
+// commit, and git reads one behind a `+`, `-` or space modifier (`%+G?`,
+// `%-GG`, `% GS`) as the same placeholder. A value with no %, no format: and
+// no tformat: is looked up by prefix among the built-in formats and the
+// repository's `pretty.<name>` aliases, and an alias can hold one, so only a
+// built-in name is taken.
+const SIGNATURE_PLACEHOLDER = /%[-+ ]?G/;
 const BUILTIN_FORMATS = Object.freeze(['oneline', 'short', 'medium', 'full', 'fuller', 'reference', 'email', 'mboxrd', 'raw']);
+// Git's revision parser reads --pretty and --format only by their exact names,
+// and their format only after `=`: a bare --pretty means medium, and a bare
+// --format is an unrecognized argument. The check does not depend on that. An
+// abbreviation (`--form=`, `--pret=`) is checked like the full name, and a
+// --format that would take its format from the next argument is refused.
+const FORMAT_OPTIONS = Object.freeze(['--pretty', '--format']);
 const checkFormat = (arg) => {
-  const match = FORMAT_ARGUMENT.exec(arg);
-  if (!match) return null;
-  const value = match[1];
-  if (value.includes('%G')) return `${arg} is refused: a %G placeholder runs gpg to check a signature`;
+  const [name] = arg.split('=', 1);
+  const option = name.length >= 3 && FORMAT_OPTIONS.find((full) => full.startsWith(name));
+  if (!option) return null;
+  if (name === arg) {
+    return option === '--format' ? `${arg} is refused: give the format in the same argument, as --format=<format>` : null;
+  }
+  const value = arg.slice(name.length + 1);
+  if (SIGNATURE_PLACEHOLDER.test(value)) return `${arg} is refused: a %G placeholder runs gpg to check a signature`;
   const userFormat = value === '' || value.startsWith('format:') || value.startsWith('tformat:') || value.includes('%');
   if (userFormat || BUILTIN_FORMATS.includes(value.toLowerCase())) return null;
   return `${arg} is refused: name a built-in format (${BUILTIN_FORMATS.join(', ')}) or give format:<placeholders>`;