diff --git a/web/element/codemirror-element.ts b/web/element/codemirror-element.ts
index ee7b9bc..98dd811 100644
--- a/web/element/codemirror-element.ts
+++ b/web/element/codemirror-element.ts
@@ -17,6 +17,8 @@
     'content-change': ValueChangedEvent;
   }
   interface HTMLElementTagNameMap {
+    // @ts-ignore TS2717: Subsequent property declarations must have the same
+    // type.
     'codemirror-element': CodeMirrorElement;
   }
 }
diff --git a/web/element/codemirror-element_test.ts b/web/element/codemirror-element_test.ts
index ca8383e..86f3f4d 100644
--- a/web/element/codemirror-element_test.ts
+++ b/web/element/codemirror-element_test.ts
@@ -15,8 +15,8 @@
       html`<codemirror-element></codemirror-element>`
     );
     element.lineNum = 123;
-    element.params = {
-      matchBrackets: true,
+    element.prefs = {
+      match_brackets: true,
     };
     await element.updateComplete;
   });
diff --git a/web/gr-editor.ts b/web/gr-editor.ts
index 05e5dbd..b211a99 100644
--- a/web/gr-editor.ts
+++ b/web/gr-editor.ts
@@ -16,7 +16,7 @@
  */
 interface CodeMirrorElement extends HTMLElement {
   lineNum?: number;
-  prefs: unknown;
+  prefs?: unknown;
   fileContent?: string;
   fileType?: string;
 }
@@ -24,6 +24,8 @@
 declare global {
   interface HTMLElementTagNameMap {
     'gr-editor': GrEditor;
+    // @ts-ignore TS2717: Subsequent property declarations must have the same
+    // type.
     'codemirror-element': CodeMirrorElement;
   }
 }
diff --git a/web/gr-editor_test.ts b/web/gr-editor_test.ts
index d44f66a..613daa4 100644
--- a/web/gr-editor_test.ts
+++ b/web/gr-editor_test.ts
@@ -51,6 +51,6 @@
       'codemirror-element'
     );
     assert.equal(cmElement.lineNum, 123);
-    assert.isTrue(cmElement.params?.matchBrackets);
+    assert.isTrue(cmElement.prefs?.match_brackets);
   });
 });