diff --git a/pkg/front_end/lib/src/fasta/incremental_compiler.dart b/pkg/front_end/lib/src/fasta/incremental_compiler.dart
index 9975660a4fd..96d190dd456 100644
--- a/pkg/front_end/lib/src/fasta/incremental_compiler.dart
+++ b/pkg/front_end/lib/src/fasta/incremental_compiler.dart
@@ -106,24 +106,30 @@ class IncrementalCompiler implements IncrementalKernelGenerator {
     Set<Uri> invalidatedFileUris = invalidatedUris.toSet();
 
     // Maps all non-platform LibraryBuilders from their import URI.
-    Map<Uri, LibraryBuilder> builders = <Uri, LibraryBuilder>{};
+    Map<Uri, SourceLibraryBuilder> builders = <Uri, SourceLibraryBuilder>{};
 
     // Invalidated URIs translated back to their import URI (package:, dart:,
     // etc.).
     List<Uri> invalidatedImportUris = <Uri>[];
 
     // Compute [builders] and [invalidatedImportUris].
-    userCode.loader.builders.forEach((Uri uri, LibraryBuilder library) {
-      if (library.loader != platform.loader) {
-        assert(library is SourceLibraryBuilder);
+    addBuilderAndInvalidateUris(Uri uri, LibraryBuilder libraryBuilder) {
+      if (libraryBuilder.loader != platform.loader) {
+        assert(libraryBuilder is SourceLibraryBuilder);
+        SourceLibraryBuilder library = libraryBuilder;
         builders[uri] = library;
         if (invalidatedFileUris.contains(uri) ||
             (uri != library.fileUri &&
                 invalidatedFileUris.contains(library.fileUri))) {
           invalidatedImportUris.add(uri);
         }
+        for (var part in library.parts) {
+          addBuilderAndInvalidateUris(part.uri, part);
+        }
       }
-    });
+    }
+
+    userCode.loader.builders.forEach(addBuilderAndInvalidateUris);
 
     SourceGraph graph = new SourceGraph(builders);
 
@@ -153,7 +159,7 @@ class IncrementalCompiler implements IncrementalKernelGenerator {
       }
     }
 
-    return builders.values.toList();
+    return builders.values.where((builder) => !builder.isPart).toList();
   }
 
   @override
diff --git a/pkg/front_end/testcases/incremental.status b/pkg/front_end/testcases/incremental.status
index 775e406cbc2..f14d52e3b38 100644
--- a/pkg/front_end/testcases/incremental.status
+++ b/pkg/front_end/testcases/incremental.status
@@ -4,7 +4,6 @@
 
 # Status file for the test suite ../test/fasta/incremental_test.dart.
 
-dartino/change_in_part.incremental: Fail # Issue 31908 (parts aren't handled correctly)
 dartino/override_field_with_method_conflict.incremental: Fail # These tests are the incremental version of tests like language_2/field_override* and language_2/override_field_method*
 dartino/override_getter_with_method_conflict.incremental: Fail # These tests are the incremental version of tests like language_2/field_override* and language_2/override_field_method*
 dartino/override_method_with_field_conflict.incremental: Fail # These tests are the incremental version of tests like language_2/field_override* and language_2/override_field_method*