diff --git a/pkg/analyzer/lib/src/dart/sdk/sdk.dart b/pkg/analyzer/lib/src/dart/sdk/sdk.dart
index a6c49083fde..cfed575fb98 100644
--- a/pkg/analyzer/lib/src/dart/sdk/sdk.dart
+++ b/pkg/analyzer/lib/src/dart/sdk/sdk.dart
@@ -651,7 +651,13 @@ class FolderBasedDartSdk extends AbstractDartSdk {
     try {
       File file = libraryDirectory.getChildAssumingFile(library.path);
       if (!relativePath.isEmpty) {
-        file = file.parent.getChildAssumingFile(relativePath);
+        File relativeFile = file.parent.getChildAssumingFile(relativePath);
+        if (relativeFile.path == file.path) {
+          // The relative file is the library, so return a Source for the
+          // library rather than the part format.
+          return file.createSource(Uri.parse(library.shortName));
+        }
+        file = relativeFile;
       }
       return file.createSource(Uri.parse(dartUri));
     } on FormatException {
diff --git a/pkg/analyzer/lib/src/summary/summarize_ast.dart b/pkg/analyzer/lib/src/summary/summarize_ast.dart
index 2ca188cf564..e1d45ce408f 100644
--- a/pkg/analyzer/lib/src/summary/summarize_ast.dart
+++ b/pkg/analyzer/lib/src/summary/summarize_ast.dart
@@ -1437,7 +1437,8 @@ class _SummarizeAstVisitor extends RecursiveAstVisitor {
 
   @override
   void visitPartOfDirective(PartOfDirective node) {
-    isCoreLibrary = node.libraryName?.name == 'dart.core';
+    isCoreLibrary = node.libraryName?.name == 'dart.core' ||
+        node.uri?.stringValue == 'core.dart';
     isPartOf = true;
   }
 
diff --git a/pkg/analyzer/test/src/context/source_test.dart b/pkg/analyzer/test/src/context/source_test.dart
index 7d63c4575bd..2857e8632ed 100644
--- a/pkg/analyzer/test/src/context/source_test.dart
+++ b/pkg/analyzer/test/src/context/source_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-library analyzer.test.src.context.source_test;
-
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/context/source.dart';
 import 'package:analyzer/src/generated/source.dart';
diff --git a/pkg/analyzer/test/src/dart/sdk/sdk_test.dart b/pkg/analyzer/test/src/dart/sdk/sdk_test.dart
index 3abf7c2625d..e2d9071139b 100644
--- a/pkg/analyzer/test/src/dart/sdk/sdk_test.dart
+++ b/pkg/analyzer/test/src/dart/sdk/sdk_test.dart
@@ -250,6 +250,17 @@ class FolderBasedDartSdkTest {
     expect(version.length > 0, isTrue);
   }
 
+  /**
+   * The "part" format should result in the same source as the non-part format
+   * when the file is the library file.
+   */
+  void test_mapDartUri_partFormatForLibrary() {
+    FolderBasedDartSdk sdk = _createDartSdk();
+    Source normalSource = sdk.mapDartUri('dart:core');
+    Source partSource = sdk.mapDartUri('dart:core/core.dart');
+    expect(partSource, normalSource);
+  }
+
   void test_useSummary_afterContextCreation() {
     FolderBasedDartSdk sdk = _createDartSdk();
     sdk.context;