diff --git a/packages/pyright-internal/src/parser/tokenizer.ts b/packages/pyright-internal/src/parser/tokenizer.ts
index 562328586787..416532935708 100644
--- a/packages/pyright-internal/src/parser/tokenizer.ts
+++ b/packages/pyright-internal/src/parser/tokenizer.ts
@@ -142,7 +142,11 @@ const _byteOrderMarker = 0xfeff;
 
 const defaultTabSize = 8;
 const magicsRegEx = /\\\s*$/;
-const typeIgnoreCommentRegEx = /((^|#)\s*)type:\s*ignore(\s*\[([\s\w-,]*)\]|\s|$)/;
+// The character class for type: ignore rule codes includes ':' so that
+// tool-namespaced codes such as "ty:unresolved-reference" are accepted.
+// pyright: ignore uses the original class since tool-namespaced codes
+// are not expected there.
+const typeIgnoreCommentRegEx = /((^|#)\s*)type:\s*ignore(\s*\[([\s\w:,-]*)\]|\s|$)/;
 const pyrightIgnoreCommentRegEx = /((^|#)\s*)pyright:\s*ignore(\s*\[([\s\w-,]*)\]|\s|$)/;
 const underscoreRegEx = /_/g;
 
diff --git a/packages/pyright-internal/src/tests/tokenizer.test.ts b/packages/pyright-internal/src/tests/tokenizer.test.ts
index d755a972498f..32f92009bbd1 100644
--- a/packages/pyright-internal/src/tests/tokenizer.test.ts
+++ b/packages/pyright-internal/src/tests/tokenizer.test.ts
@@ -1815,6 +1815,33 @@ test('TypeIgnoreLine2', () => {
     assert.equal(results.tokens.contains(42), false);
 });
 
+// Regression test for https://github.com/microsoft/pyright/issues/11345.
+// type: ignore comments containing tool-namespaced codes (e.g. "ty:rule-name")
+// must be recognised as type: ignore comments.
+test('TypeIgnoreNamespacedCode', () => {
+    const t = new Tokenizer();
+    // Single namespaced code.
+    const results = t.tokenize('a = 1  # type: ignore[ty:unresolved-reference]');
+    assert.equal(results.typeIgnoreLines.size, 1);
+    assert(results.typeIgnoreLines.has(0));
+    const rules = results.typeIgnoreLines.get(0)!.rulesList;
+    assert(rules !== undefined);
+    assert.equal(rules.length, 1);
+    assert.equal(rules[0].text, 'ty:unresolved-reference');
+});
+
+test('TypeIgnoreMixedNamespacedCodes', () => {
+    const t = new Tokenizer();
+    // Mix of plain and namespaced codes.
+    const results = t.tokenize('a = 1  # type: ignore[name-defined, ty:unresolved-reference]');
+    assert.equal(results.typeIgnoreLines.size, 1);
+    const rules = results.typeIgnoreLines.get(0)!.rulesList;
+    assert(rules !== undefined);
+    assert.equal(rules.length, 2);
+    assert.equal(rules[0].text, 'name-defined');
+    assert.equal(rules[1].text, 'ty:unresolved-reference');
+});
+
 test('Constructor', () => {
     const t = new Tokenizer();
     const results = t.tokenize('def constructor');