diff --git a/src/vs/vscode.proposed.d.ts b/src/vs/vscode.proposed.d.ts
index 2282858b43c..af1b501c6bb 100644
--- a/src/vs/vscode.proposed.d.ts
+++ b/src/vs/vscode.proposed.d.ts
@@ -11,14 +11,18 @@ declare module 'vscode' {
 		export function sampleFunction(): Thenable<any>;
 	}
 
+	//#region Joh - https://github.com/Microsoft/vscode/issues/1800
+
 	export namespace languages {
 
 		/**
 		 *
 		 */
-		export function changeLanguage(document: TextDocument, languageId: string): Thenable<TextDocument>;
+		export function setTextDocumentLanguage(document: TextDocument, languageId: string): Thenable<TextDocument>;
 	}
 
+	//#endregion
+
 	//#region Joh - read/write in chunks
 
 	export interface FileSystemProvider {
diff --git a/src/vs/workbench/api/node/extHost.api.impl.ts b/src/vs/workbench/api/node/extHost.api.impl.ts
index 479c30559ad..e8ba986c4bf 100644
--- a/src/vs/workbench/api/node/extHost.api.impl.ts
+++ b/src/vs/workbench/api/node/extHost.api.impl.ts
@@ -269,7 +269,7 @@ export function createApiFactory(
 			getLanguages(): Thenable<string[]> {
 				return extHostLanguages.getLanguages();
 			},
-			changeLanguage(document: vscode.TextDocument, languageId: string): Thenable<vscode.TextDocument> {
+			setTextDocumentLanguage(document: vscode.TextDocument, languageId: string): Thenable<vscode.TextDocument> {
 				checkProposedApiEnabled(extension);
 				return extHostLanguages.changeLanguage(document.uri, languageId);
 			},