diff --git a/client-src/elements/chromedash-ot-creation-page.ts b/client-src/elements/chromedash-ot-creation-page.ts
index 067344a4..e7c7c81a 100644
--- a/client-src/elements/chromedash-ot-creation-page.ts
+++ b/client-src/elements/chromedash-ot-creation-page.ts
@@ -356,15 +356,16 @@ export class ChromedashOTCreationPage extends LitElement {
       this.featureId
     );
     // We only need the single stage changes.
-    const stageSubmitBody = featureSubmitBody.stages[0] as Object;
+    const stageSubmitBody = featureSubmitBody.stages[0];
 
-    // Add on the appropriate use counter prefix.
-    const useCounterPrefix =
-      this.webfeatureUseCounterType === USE_COUNTER_TYPE_WEBFEATURE
-        ? ''
-        : 'WebDXFeature::';
-    stageSubmitBody['ot_webfeature_use_counter'].value =
-      `${useCounterPrefix}${stageSubmitBody['ot_webfeature_use_counter'].value}`;
+    if ('ot_webfeature_use_counter' in stageSubmitBody) {
+      // Add on the appropriate use counter prefix.
+      const useCounterPrefix =
+        this.webfeatureUseCounterType === USE_COUNTER_TYPE_WEBFEATURE
+          ? ''
+          : 'WebDXFeature::';
+      stageSubmitBody.ot_webfeature_use_counter.value = `${useCounterPrefix}${stageSubmitBody.ot_webfeature_use_counter.value}`;
+    }
 
     this.submitting = true;
     window.csClient
diff --git a/client-src/elements/utils.ts b/client-src/elements/utils.ts
index d6172174..dea7db05 100644
--- a/client-src/elements/utils.ts
+++ b/client-src/elements/utils.ts
@@ -541,21 +541,22 @@ export interface FieldInfo {
   checkMessage?: string;
 }
 
-/**
- * @typedef {Object} UpdateSubmitBody
- * @property {Object.<string, *>} feature_changes An object with feature changes.
- *   key=field name, value=new field value.
- * @property {Array.<Object>} stages The list of changes to specific stages.
- * @property {boolean} has_changes Whether any valid changes are present for submission.
- */
+interface UpdateSubmitBody {
+  feature_changes: FeatureUpdateInfo;
+  stages: StageUpdateInfo[];
+  has_changes: boolean;
+}
 
-/**
- * Prepare feature/stage changes to be submitted.
- * @param {Array.<FieldInfo>} fieldValues List of fields in the form.
- * @param {number} featureId The ID of the feature being updated.
- * @return {UpdateSubmitBody} Formatted body of new PATCH request.
- */
-export function formatFeatureChanges(fieldValues, featureId) {
+interface StageUpdateInfo {
+  [stageField: string]: any;
+}
+
+interface FeatureUpdateInfo {
+  [featureField: string]: any;
+}
+
+// Prepare feature/stage changes to be submitted.
+export function formatFeatureChanges(fieldValues, featureId): UpdateSubmitBody {
   let hasChanges = false;
   const featureChanges = {id: featureId};
   // Multiple stages can be mutated, so this object is a stage of stages.