diff --git a/web/src/elements/forms/Form.ts b/web/src/elements/forms/Form.ts
index 47eee9cc06..3d18d095fa 100644
--- a/web/src/elements/forms/Form.ts
+++ b/web/src/elements/forms/Form.ts
@@ -114,9 +114,10 @@ export function serializeForm<T = Record<string, unknown>>(elements: Iterable<AK
             }
 
             if (inputElement.type === "datetime-local") {
+                const valueAsNumber = inputElement.valueAsNumber;
                 return assignValue(
                     inputElement,
-                    dateToUTC(new Date(inputElement.valueAsNumber)),
+                    isNaN(valueAsNumber) ? null : dateToUTC(new Date(valueAsNumber)),
                     json,
                 );
             }
@@ -124,7 +125,12 @@ export function serializeForm<T = Record<string, unknown>>(elements: Iterable<AK
             if ("type" in inputElement.dataset && inputElement.dataset.type === "datetime-local") {
                 // Workaround for Firefox <93, since 92 and older don't support
                 // datetime-local fields
-                return assignValue(inputElement, dateToUTC(new Date(inputElement.value)), json);
+                const date = new Date(inputElement.value);
+                return assignValue(
+                    inputElement,
+                    isNaN(date.getTime()) ? null : dateToUTC(date),
+                    json,
+                );
             }
 
             if (inputElement.type === "checkbox") {