diff --git a/pkg/analyzer/lib/src/dart/sdk/sdk.dart b/pkg/analyzer/lib/src/dart/sdk/sdk.dart
index 35fb194..b23e091 100644
--- a/pkg/analyzer/lib/src/dart/sdk/sdk.dart
+++ b/pkg/analyzer/lib/src/dart/sdk/sdk.dart
@@ -46,17 +46,6 @@
   @override
   List<String> get uris => libraryMap.uris;
 
-  /// Add the extensions from one or more sdk extension files to this sdk. The
-  /// [extensions] should be a table mapping the names of extensions to the
-  /// paths where those extensions can be found.
-  void addExtensions(Map<String, String> extensions) {
-    extensions.forEach((String uri, String path) {
-      SdkLibraryImpl library = SdkLibraryImpl(uri);
-      library.path = path;
-      libraryMap.setLibrary(uri, library);
-    });
-  }
-
   /// Return info for debugging https://github.com/dart-lang/sdk/issues/35226.
   Map<String, Object> debugInfo() {
     return <String, Object>{
diff --git a/pkg/analyzer/test/src/dart/sdk/sdk_test.dart b/pkg/analyzer/test/src/dart/sdk/sdk_test.dart
index 6af1989..40d24dd 100644
--- a/pkg/analyzer/test/src/dart/sdk/sdk_test.dart
+++ b/pkg/analyzer/test/src/dart/sdk/sdk_test.dart
@@ -122,17 +122,6 @@
 
 @reflectiveTest
 class FolderBasedDartSdkTest with ResourceProviderMixin {
-  void test_addExtensions() {
-    FolderBasedDartSdk sdk = _createDartSdk();
-    String uri = 'dart:my.internal';
-    sdk.addExtensions({uri: '/Users/user/dart/my.dart'});
-    expect(sdk.mapDartUri(uri), isNotNull);
-    // The `shortName` property must include the `dart:` prefix.
-    expect(sdk.sdkLibraries, contains(predicate((SdkLibrary library) {
-      return library.shortName == uri;
-    })));
-  }
-
   void test_creation() {
     FolderBasedDartSdk sdk = _createDartSdk();
     expect(sdk, isNotNull);