diff --git a/source_gen/source_gen/source_gen/CHANGELOG.md b/source_gen/source_gen/source_gen/CHANGELOG.md
index 82735ab51..6bd6b8ad9 100644
--- a/source_gen/source_gen/source_gen/CHANGELOG.md
+++ b/source_gen/source_gen/source_gen/CHANGELOG.md
@@ -1,3 +1,8 @@
+## 1.3.1
+
+* Always use a Uri in `part of` directives (previously a name would be used if
+  the library had a non-empty one).
+
 ## 1.3.0
 
 * Add support for `build_extensions` configuration of builders producing
diff --git a/source_gen/source_gen/source_gen/lib/builder.dart b/source_gen/source_gen/source_gen/lib/builder.dart
index 80688b320..7a7a3b202 100644
--- a/source_gen/source_gen/source_gen/lib/builder.dart
+++ b/source_gen/source_gen/source_gen/lib/builder.dart
@@ -120,7 +120,7 @@ class CombiningBuilder implements Builder {
 
     final inputLibrary = await buildStep.inputLibrary;
     final outputId = buildStep.allowedOutputs.single;
-    final partOf = nameOfPartial(inputLibrary, buildStep.inputId, outputId);
+    final partOfUri = uriOfPartial(inputLibrary, buildStep.inputId, outputId);
 
     // Ensure that the input has a correct `part` statement.
     final libraryUnit =
@@ -143,7 +143,7 @@ class CombiningBuilder implements Builder {
     final output = '''
 $defaultFileHeader
 ${languageOverrideForLibrary(inputLibrary)}$ignoreForFile$preamble
-part of $partOf;
+part of '$partOfUri';
 
 $assets
 ''';
diff --git a/source_gen/source_gen/source_gen/lib/src/builder.dart b/source_gen/source_gen/source_gen/lib/src/builder.dart
index 6c5054196..e3808282f 100644
--- a/source_gen/source_gen/source_gen/lib/src/builder.dart
+++ b/source_gen/source_gen/source_gen/lib/src/builder.dart
@@ -124,13 +124,13 @@ class _Builder extends Builder {
 
     if (!_isLibraryBuilder) {
       final asset = buildStep.inputId;
-      final name = nameOfPartial(library, asset, outputId);
+      final partOfUri = uriOfPartial(library, asset, outputId);
       contentBuffer.writeln();
 
       if (this is PartBuilder) {
         contentBuffer
           ..write(languageOverrideForLibrary(library))
-          ..writeln('part of $name;');
+          ..writeln('part of \'$partOfUri\';');
         final part = computePartUrl(buildStep.inputId, outputId);
 
         final libraryUnit =
diff --git a/source_gen/source_gen/source_gen/lib/src/utils.dart b/source_gen/source_gen/source_gen/lib/src/utils.dart
index 1ad029165..f15fd596b 100644
--- a/source_gen/source_gen/source_gen/lib/src/utils.dart
+++ b/source_gen/source_gen/source_gen/lib/src/utils.dart
@@ -43,29 +43,10 @@ bool hasExpectedPartDirective(CompilationUnit unit, String part) =>
         .whereType<PartDirective>()
         .any((e) => e.uri.stringValue == part);
 
-/// Returns a name suitable for `part of "..."` when pointing to [element].
-String nameOfPartial(LibraryElement element, AssetId source, AssetId output) {
-  if (element.name.isNotEmpty) {
-    return element.name;
-  }
-
+/// Returns a uri suitable for `part of "..."` when pointing to [element].
+String uriOfPartial(LibraryElement element, AssetId source, AssetId output) {
   assert(source.package == output.package);
-  final relativeSourceUri =
-      p.url.relative(source.path, from: p.url.dirname(output.path));
-  return '\'$relativeSourceUri\'';
-}
-
-/// Returns a suggested library identifier based on [source] path and package.
-String suggestLibraryName(AssetId source) {
-  // lib/test.dart --> [lib/test.dart]
-  final parts = source.path.split('/');
-  // [lib/test.dart] --> [lib/test]
-  parts[parts.length - 1] = parts.last.split('.').first;
-  // [lib/test] --> [test]
-  if (parts.first == 'lib') {
-    parts.removeAt(0);
-  }
-  return '${source.package}.${parts.join('.')}';
+  return p.url.relative(source.path, from: p.url.dirname(output.path));
 }
 
 /// Returns what 'part "..."' URL is needed to import [output] from [input].
diff --git a/source_gen/source_gen/source_gen/pubspec.yaml b/source_gen/source_gen/source_gen/pubspec.yaml
index b841ab869..19def4ee3 100644
--- a/source_gen/source_gen/source_gen/pubspec.yaml
+++ b/source_gen/source_gen/source_gen/pubspec.yaml
@@ -1,5 +1,5 @@
 name: source_gen
-version: 1.3.0
+version: 1.3.1
 description: >-
   Source code generation builders and utilities for the Dart build system
 repository: https://github.com/dart-lang/source_gen/tree/master/source_gen
diff --git a/source_gen/source_gen/source_gen/test/builder_test.dart b/source_gen/source_gen/source_gen/test/builder_test.dart
index cf53fda3a..9a0198027 100644
--- a/source_gen/source_gen/source_gen/test/builder_test.dart
+++ b/source_gen/source_gen/source_gen/test/builder_test.dart
@@ -519,7 +519,7 @@ part "a.g.dart";
 // GENERATED CODE - DO NOT MODIFY BY HAND
 // @dart=2.12
 
-part of a;
+part of 'a.dart';
 
 some generated content
 ''',
@@ -668,7 +668,7 @@ some generated content
               r'''
 // ignore_for_file: lines_longer_than_80_chars, prefer_expression_function_bodies
 
-part of a;
+part of 'a.dart';
 
 bar generated content
 
@@ -703,7 +703,7 @@ foo generated content
 
 // bar
 
-part of a;
+part of 'a.dart';
 
 bar generated content
 
@@ -970,7 +970,7 @@ class MyGoodError { }
 ''';
 
 const _testLibPartContent = r'''
-part of test_lib;
+part of 'test_lib.dart';
 final int bar = 42;
 class Customer { }
 ''';
@@ -987,7 +987,7 @@ final int foo = 42
 
 const _testGenPartContent = r'''// GENERATED CODE - DO NOT MODIFY BY HAND
 
-part of test_lib;
+part of 'test_lib.dart';
 
 // **************************************************************************
 // CommentGenerator
@@ -1000,7 +1000,7 @@ part of test_lib;
 const _testGenPartContentForLibrary =
     r'''// GENERATED CODE - DO NOT MODIFY BY HAND
 
-part of test_lib;
+part of 'test_lib.dart';
 
 // **************************************************************************
 // CommentGenerator
@@ -1022,7 +1022,7 @@ const _testGenStandaloneContent = r'''// GENERATED CODE - DO NOT MODIFY BY HAND
 const _testGenPartContentForClassesAndLibrary =
     r'''// GENERATED CODE - DO NOT MODIFY BY HAND
 
-part of test_lib;
+part of 'test_lib.dart';
 
 // **************************************************************************
 // CommentGenerator
@@ -1047,7 +1047,7 @@ part of 'test_lib.dart';
 
 const _whitespaceTrimmed = r'''// GENERATED CODE - DO NOT MODIFY BY HAND
 
-part of test_lib;
+part of 'test_lib.dart';
 
 // **************************************************************************
 // Generator: Literal