diff --git a/spec/text-editor-component-spec.js b/spec/text-editor-component-spec.js
index 992785d6e..d848ffc9d 100644
--- a/spec/text-editor-component-spec.js
+++ b/spec/text-editor-component-spec.js
@@ -4478,6 +4478,7 @@ function buildEditor (params = {}) {
   for (const paramName of ['mini', 'autoHeight', 'autoWidth', 'lineNumberGutterVisible', 'showLineNumbers', 'placeholderText', 'softWrapped', 'scrollSensitivity']) {
     if (params[paramName] != null) editorParams[paramName] = params[paramName]
   }
+  atom.grammars.assignLanguageModeToBuffer(buffer)
   const editor = new TextEditor(editorParams)
   editor.testAutoscrollRequests = []
   editor.onDidRequestAutoscroll((request) => { editor.testAutoscrollRequests.push(request) })