@@ -94,6 +94,7 @@ export function renamedSince(
   for (const [file, origin] of origins) {
     if (origin !== null) renamed.set(file, origin);
   }
+  const claimedOrigins = new Set(renamed.values());
   const aggregate = git(repoRoot, [
     '-c',
     'diff.renameLimit=0',
@@ -109,7 +110,10 @@ export function renamedSince(
     const from = aggregate[index++];
     if (kind?.startsWith('R')) {
       const to = aggregate[index++];
-      if (from && to && !renamed.has(to) && !ended.has(to)) renamed.set(to, from);
+      if (from && to && !renamed.has(to) && !ended.has(to) && !claimedOrigins.has(from)) {
+        renamed.set(to, from);
+        claimedOrigins.add(from);
+      }
     }
   }
   return renamed;
 
@@ -560,6 +560,16 @@ test('a new file at a moved source cannot claim the original lineage when rename
   const paired = renamedSince(repo, base, 'HEAD');
   expect(paired.get('packages/demo/src/moved.ts')).toBe(original);
   expect(paired.has('packages/demo/src/new.ts')).toBe(false);
+  fs.appendFileSync(
+    path.join(repo, 'packages/demo/src/moved.ts'),
+    '// public API documentation\n'.repeat(100),
+  );
+  fs.writeFileSync(path.join(repo, 'packages/demo/src/copy.ts'), 'export const a = 1;\n');
+  execFileSync('git', ['add', '.'], { cwd: repo });
+  execFileSync('git', ['commit', '-qm', 'copy old content'], { cwd: repo });
+  const withCopy = renamedSince(repo, base, 'HEAD');
+  expect(withCopy.get('packages/demo/src/moved.ts')).toBe(original);
+  expect(withCopy.has('packages/demo/src/copy.ts')).toBe(false);
 });
 
 test('rename detection survives a git mv with an edit and a hostile renameLimit', () => {
Original file line number	Diff line number	Diff line change
`@@ -94,6 +94,7 @@ export function renamedSince(`
`94`	`94`	`for (const [file, origin] of origins) {`
`95`	`95`	`if (origin !== null) renamed.set(file, origin);`
`96`	`96`	`}`
	`97`	`+ const claimedOrigins = new Set(renamed.values());`
`97`	`98`	`const aggregate = git(repoRoot, [`
`98`	`99`	`'-c',`
`99`	`100`	`'diff.renameLimit=0',`
`@@ -109,7 +110,10 @@ export function renamedSince(`
`109`	`110`	`const from = aggregate[index++];`
`110`	`111`	`if (kind?.startsWith('R')) {`
`111`	`112`	`const to = aggregate[index++];`
`112`		`- if (from && to && !renamed.has(to) && !ended.has(to)) renamed.set(to, from);`
	`113`	`+ if (from && to && !renamed.has(to) && !ended.has(to) && !claimedOrigins.has(from)) {`
	`114`	`+ renamed.set(to, from);`
	`115`	`+ claimedOrigins.add(from);`
	`116`	`+ }`
`113`	`117`	`}`
`114`	`118`	`}`
`115`	`119`	`return renamed;`