diff --git a/frontend/lib/util/form.test.ts b/frontend/lib/util/form.test.ts
index 99288b3ed..89d6881cf 100644
--- a/frontend/lib/util/form.test.ts
+++ b/frontend/lib/util/form.test.ts
@@ -37,7 +37,7 @@ describe("Form", () => {
 
     // Number required
     [{ type: "number", required: true }, "", "FORM_VALIDATION_RESULT_REQUIRED", undefined],
-    // FIXME in issue #824 [{ type: "number", required: false }, "", undefined, undefined],
+    [{ type: "number", required: false }, "", undefined, undefined],
 
     // Number min/max
     [{ type: "number", min: 3 }, "2", "FORM_VALIDATION_RESULT_MIN", undefined],
@@ -54,7 +54,7 @@ describe("Form", () => {
 
     // Number isFormatted required
     [{ type: "number", isFormatted: true, required: true }, "", "FORM_VALIDATION_RESULT_REQUIRED", undefined],
-    // FIXME in issue #824 [{ type: "number", isFormatted: true , required: false }, "", undefined, undefined],
+    [{ type: "number", isFormatted: true, required: false }, "", undefined, undefined],
   ])("processForm for field type %j with input %j should return %j, %j", (field, inputValue, error, value) => {
     type RequestObject = { field: FieldValue<typeof field> };
     const formFields: FormFields<RequestObject> = { field };
diff --git a/frontend/lib/util/form.ts b/frontend/lib/util/form.ts
index a6235d088..c17ee0f6c 100644
--- a/frontend/lib/util/form.ts
+++ b/frontend/lib/util/form.ts
@@ -67,6 +67,10 @@ export function processForm<RequestObject>(
 
     switch (field.type) {
       case "number": {
+        if (!field.required && value === "") {
+          value = undefined;
+          break;
+        }
         const parsedValue = field.isFormatted ? deformatNumber(value) : parseIntUserInput(value);
         //parseInt is used in deformatNumber, the result is a number or NaN.
         if (parsedValue === undefined || Number.isNaN(parsedValue)) {
@@ -121,6 +125,8 @@ export function validateFormValue(field: AnyFormField, value: string | number |
         if (field.max && value > field.max) {
           return "FORM_VALIDATION_RESULT_MAX";
         }
+      } else if (!field.required && value === undefined) {
+        return null;
       } else {
         return "FORM_VALIDATION_RESULT_INVALID_TYPE";
       }