diff --git a/authentik/core/api/tokens.py b/authentik/core/api/tokens.py
index 917f30937652..334b5f735a8d 100644
--- a/authentik/core/api/tokens.py
+++ b/authentik/core/api/tokens.py
@@ -76,7 +76,8 @@ def validate(self, attrs: dict[Any, str]) -> dict[Any, str]:
                 except ValueError:
                     pass
 
-            if "expires" in attrs and attrs.get("expires") > max_token_lifetime_dt:
+            expires = attrs.get("expires")
+            if expires is not None and expires > max_token_lifetime_dt:
                 raise ValidationError(
                     {
                         "expires": (
diff --git a/web/src/elements/forms/Form.ts b/web/src/elements/forms/Form.ts
index e7967a38b106..b23d44816c13 100644
--- a/web/src/elements/forms/Form.ts
+++ b/web/src/elements/forms/Form.ts
@@ -117,7 +117,7 @@ export function serializeForm<T = Record<string, unknown>>(elements: Iterable<AK
                 const valueAsNumber = inputElement.valueAsNumber;
                 return assignValue(
                     inputElement,
-                    isNaN(valueAsNumber) ? null : dateToUTC(new Date(valueAsNumber)),
+                    isNaN(valueAsNumber) ? undefined : dateToUTC(new Date(valueAsNumber)),
                     json,
                 );
             }
@@ -128,7 +128,7 @@ export function serializeForm<T = Record<string, unknown>>(elements: Iterable<AK
                 const date = new Date(inputElement.value);
                 return assignValue(
                     inputElement,
-                    isNaN(date.getTime()) ? null : dateToUTC(date),
+                    isNaN(date.getTime()) ? undefined : dateToUTC(date),
                     json,
                 );
             }