diff --git a/src/components/shared/SourceView-codemirror.ts b/src/components/shared/SourceView-codemirror.ts
index 65f8c5dab9..ae88c8d4ff 100644
--- a/src/components/shared/SourceView-codemirror.ts
+++ b/src/components/shared/SourceView-codemirror.ts
@@ -86,7 +86,7 @@ function _languageExtForPath(path: string | null): LanguageSupport | [] {
 
 // Adjustments to make a CodeMirror editor work as a non-editable code viewer.
 const codeViewerExtension = [
-  // Make the editor non-editable.
+  EditorState.readOnly.of(true),
   EditorView.editable.of(false),
   // Allow tabbing to the view (to an element *inside* the scroller so that the
   // up / down keys trigger scrolling), and take focus on mousedown.
diff --git a/src/test/components/__snapshots__/BottomBox.test.tsx.snap b/src/test/components/__snapshots__/BottomBox.test.tsx.snap
index a4bc6089ff..d48ed6cf9b 100644
--- a/src/test/components/__snapshots__/BottomBox.test.tsx.snap
+++ b/src/test/components/__snapshots__/BottomBox.test.tsx.snap
@@ -65,6 +65,7 @@ exports[`BottomBox should show the assembly view when pressing the toggle button
 exports[`BottomBox should show the source view when a line in the tree view is double-clicked 1`] = `
 <div
   aria-multiline="true"
+  aria-readonly="true"
   autocapitalize="off"
   autocorrect="off"
   class="cm-content"