diff --git a/lib/src/rules/library_private_types_in_public_api.dart b/lib/src/rules/library_private_types_in_public_api.dart
index 050a327fe..26043d78e 100644
--- a/lib/src/rules/library_private_types_in_public_api.dart
+++ b/lib/src/rules/library_private_types_in_public_api.dart
@@ -132,8 +132,20 @@ class Validator extends SimpleAstVisitor<void> {
     node.members.accept(this);
   }
 
+  @override
+  void visitExtensionTypeDeclaration(ExtensionTypeDeclaration node) {
+    if (Identifier.isPrivateName(node.name.lexeme)) return;
+    node.typeParameters?.accept(this);
+    var representation = node.representation;
+    if (!Identifier.isPrivateName(representation.fieldName.lexeme)) {
+      representation.fieldType.accept(this);
+    }
+    node.members.accept(this);
+  }
+
   @override
   void visitFieldDeclaration(FieldDeclaration node) {
+    if (node.isInvalidExtensionTypeField) return;
     if (node.fields.variables
         .any((field) => !Identifier.isPrivateName(field.name.lexeme))) {
       node.fields.type?.accept(this);
diff --git a/lib/src/rules/public_member_api_docs.dart b/lib/src/rules/public_member_api_docs.dart
index a8d21477d..1d433d76f 100644
--- a/lib/src/rules/public_member_api_docs.dart
+++ b/lib/src/rules/public_member_api_docs.dart
@@ -172,13 +172,6 @@ class _Visitor extends SimpleAstVisitor {
     _visitMembers(node, node.name, node.members);
   }
 
-  @override
-  void visitExtensionTypeDeclaration(ExtensionTypeDeclaration node) {
-    var element = node.declaredElement;
-    if (element == null || element.hasInternal) return;
-    _visitMembers(node, node.name, node.members);
-  }
-
   @override
   void visitClassTypeAlias(ClassTypeAlias node) {
     if (!isPrivate(node.name)) {
@@ -272,6 +265,13 @@ class _Visitor extends SimpleAstVisitor {
     checkMethods(node.members);
   }
 
+  @override
+  void visitExtensionTypeDeclaration(ExtensionTypeDeclaration node) {
+    var element = node.declaredElement;
+    if (element == null || element.hasInternal) return;
+    _visitMembers(node, node.name, node.members);
+  }
+
   @override
   void visitFieldDeclaration(FieldDeclaration node) {
     // todo(pq): update this to be called from the parent (like with visitMembers)
diff --git a/test/rules/library_private_types_in_public_api_test.dart b/test/rules/library_private_types_in_public_api_test.dart
index f65f08d5a..ecc17da4a 100644
--- a/test/rules/library_private_types_in_public_api_test.dart
+++ b/test/rules/library_private_types_in_public_api_test.dart
@@ -9,6 +9,7 @@ import '../rule_test_support.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(LibraryPrivateTypesInPublicApiEnumTest);
+    defineReflectiveTests(LibraryPrivateTypesInPublicApiExtensionTypeTest);
     defineReflectiveTests(LibraryPrivateTypesInPublicApiSuperParamTest);
   });
 }
@@ -84,6 +85,140 @@ sealed class E {
   }
 }
 
+@reflectiveTest
+class LibraryPrivateTypesInPublicApiExtensionTypeTest extends LintRuleTest {
+  @override
+  List<String> get experiments => ['inline-class'];
+
+  @override
+  String get lintRule => 'library_private_types_in_public_api';
+
+  test_constructorParam() async {
+    await assertDiagnostics(r'''
+class _C {}
+extension type E(Object o) {
+  E.e(_C c) : o = c;
+}
+''', [
+      lint(47, 2),
+    ]);
+  }
+
+  test_extensionTypeDeclaration_representation() async {
+    await assertDiagnostics(r'''
+class _C {}
+extension type E(_C c) {}
+''', [
+      lint(29, 2),
+    ]);
+  }
+
+  test_extensionTypeDeclaration_representation_private() async {
+    await assertNoDiagnostics(r'''
+class _C {}
+extension type E(_C _c) {}
+''');
+  }
+
+  test_extensionTypeDeclaration_typeParam() async {
+    await assertDiagnostics(r'''
+class _C {}
+extension type E<T extends _C>(Object o) {}
+''', [
+      lint(39, 2),
+    ]);
+  }
+
+  test_field_instance() async {
+    await assertDiagnostics(r'''
+class _C {}
+extension type E(Object o) {
+  _C? c;
+}
+''', [
+      // No lint.
+      // todo(pq): add compilation error once reported
+    ]);
+  }
+
+  test_field_static() async {
+    await assertDiagnostics(r'''
+class _C {}
+extension type E(Object o) {
+  static _C? c;
+}
+''', [
+      lint(50, 2),
+    ]);
+  }
+
+  test_method_instance_param() async {
+    await assertDiagnostics(r'''
+class _C {}
+extension type E(Object o) {
+  m(_C c){}
+}
+''', [
+      lint(45, 2),
+    ]);
+  }
+
+  test_method_instance_private_param() async {
+    await assertDiagnostics(r'''
+class _C {}
+extension type E(Object o) {
+  _m(_C c){}
+}
+''', [
+      error(WarningCode.UNUSED_ELEMENT, 43, 2),
+    ]);
+  }
+
+  test_method_instance_returnType() async {
+    await assertDiagnostics(r'''
+class _C {}
+extension type E(Object o) {
+  _C? m() => null;
+}
+''', [
+      lint(43, 2),
+    ]);
+  }
+
+  test_method_static_param() async {
+    await assertDiagnostics(r'''
+class _C {}
+extension type E(Object o) {
+  static m(_C c){}
+}
+''', [
+      lint(52, 2),
+    ]);
+  }
+
+  test_method_static_private_returnType() async {
+    await assertDiagnostics(r'''
+class _C {}
+extension type E(Object o) {
+  static _C? _m() => null;
+}
+''', [
+      error(WarningCode.UNUSED_ELEMENT, 54, 2),
+    ]);
+  }
+
+  test_method_static_returnType() async {
+    await assertDiagnostics(r'''
+class _C {}
+extension type E(Object o) {
+  static _C? m() => null;
+}
+''', [
+      lint(50, 2),
+    ]);
+  }
+}
+
 @reflectiveTest
 class LibraryPrivateTypesInPublicApiSuperParamTest extends LintRuleTest {
   @override