diff --git a/src/MediaWiki/SchemaEditAction.php b/src/MediaWiki/SchemaEditAction.php
index c216e5e..83473bc 100644
--- a/src/MediaWiki/SchemaEditAction.php
+++ b/src/MediaWiki/SchemaEditAction.php
@@ -3,12 +3,21 @@
 namespace Wikibase\Schema\MediaWiki;
 
 use CommentStoreComment;
+use Content;
 use Deserializers\Exceptions\DeserializationException;
 use FormAction;
+use Revision;
 use RuntimeException;
 use Status;
+use Wikibase\DataModel\Term\AliasGroup;
+use Wikibase\DataModel\Term\AliasGroupList;
+use Wikibase\DataModel\Term\Fingerprint;
+use Wikibase\DataModel\Term\Term;
+use Wikibase\DataModel\Term\TermList;
 use Wikibase\Schema\DataModel\Schema;
 use Wikibase\Schema\Deserializers\DeserializerFactory;
+use Wikibase\Schema\Diff\SchemaDiffer;
+use Wikibase\Schema\Diff\SchemaPatcher;
 use Wikibase\Schema\MediaWiki\Content\WikibaseSchemaContent;
 
 /**
@@ -53,48 +62,26 @@ class SchemaEditAction extends FormAction {
 	}
 
 	protected function getFormFields() {
-		/** @var WikibaseSchemaContent $content */
-		$content = $this->getContext()->getWikiPage()->getContent();
-		if ( !$content ) {
-			throw new RuntimeException( $this->msg( 'wikibaseschema-error-schemadeleted' ) );
-		}
+		$undo = $this->getRequest()->getInt( 'undo' );
+		$undoafter = $this->getRequest()->getInt( 'undoafter' );
+		if ( $undo > 0 && $undoafter > 0 ) {
+			$olderContent = Revision::newFromId( $undo )->getContent();
+			$newerContent = Revision::newFromId( $undoafter )->getContent();
+			$latestContent = $this->getContext()->getWikiPage()->getContent();
 
-		$deserializer = DeserializerFactory::newSchemaDeserializer();
-		$serializedContent = json_decode( $content->getText(), true );
-		try {
-			$schema = $deserializer->deserialize( $serializedContent );
-		} catch ( DeserializationException $e ) {
-			// FIXME remove this try catch by 2019-02-11 !
-			return [
-				'warning' => [
-					'type' => 'info',
-					'default' => 'FIXME: Please remove this workaround in SchemaEditAction::getFormFields!',
-					'cssclass' => 'warning'
-				],
-				'label' => [
-					'type' => 'text',
-					'default' => $serializedContent[ 'labels' ][ 'en' ],
-					'label-message' => 'wikibaseschema-editpage-label-inputlabel',
-					'placeholder-message' => 'wikibaseschema-label-edit-placeholder',
-				],
-				'description' => [
-					'type' => 'text',
-					'default' => $serializedContent[ 'descriptions' ][ 'en' ],
-					'label-message' => 'wikibaseschema-editpage-description-inputlabel',
-					'placeholder-message' => 'wikibaseschema-description-edit-placeholder',
-				],
-				'aliases' => [
-					'type' => 'text',
-					'default' => implode( ' | ', $serializedContent[ 'aliases' ][ 'en' ] ),
-					'label-message' => 'wikibaseschema-editpage-aliases-inputlabel',
-					'placeholder-message' => 'wikibaseschema-aliases-edit-placeholder',
-				],
-				'schema' => [
-					'type' => 'textarea',
-					'default' => $serializedContent[ 'schema' ],
-					'label-message' => 'wikibaseschema-editpage-schema-inputlabel',
-				],
-			];
+			$diff = ( new SchemaDiffer() )->diffSchemas(
+				$this->contentToSchema( $olderContent ),
+				$this->contentToSchema( $newerContent )
+			);
+
+			$schema = $this->contentToSchema( $latestContent );
+			( new SchemaPatcher() )->patchSchema(
+				$schema,
+				$diff
+			);
+		} else {
+			$content = $this->getContext()->getWikiPage()->getContent();
+			$schema = $this->contentToSchema( $content );
 		}
 
 		return [
@@ -124,6 +111,36 @@ class SchemaEditAction extends FormAction {
 		];
 	}
 
+	private function contentToSchema( Content $content = null ) {
+		if ( !$content ) {
+			throw new RuntimeException( $this->msg( 'wikibaseschema-error-schemadeleted' ) );
+		}
+		if ( !( $content instanceof WikibaseSchemaContent ) ) {
+			throw new RuntimeException( 'internal error, unexpected content type' );
+		}
+
+		$deserializer = DeserializerFactory::newSchemaDeserializer();
+		$serializedContent = json_decode( $content->getText(), true );
+		try {
+			return $deserializer->deserialize( $serializedContent );
+		} catch ( DeserializationException $e ) {
+			return new Schema(
+				$serializedContent['schema'],
+				new Fingerprint(
+					new TermList( [
+						new Term( 'en', $serializedContent[ 'labels' ][ 'en' ] )
+					] ),
+					new TermList( [
+						new Term( 'en', $serializedContent[ 'descriptions' ][ 'en' ] )
+					] ),
+					new AliasGroupList( [
+						new AliasGroup( 'en', $serializedContent[ 'aliases' ][ 'en' ] )
+					] )
+				)
+			);
+		}
+	}
+
 	protected function usesOOUI() {
 		return true;
 	}