diff --git a/apps/scandic-web/components/HotelReservation/EnterDetails/Details/Multiroom/index.tsx b/apps/scandic-web/components/HotelReservation/EnterDetails/Details/Multiroom/index.tsx
index 63af2242c..5b79eed45 100644
--- a/apps/scandic-web/components/HotelReservation/EnterDetails/Details/Multiroom/index.tsx
+++ b/apps/scandic-web/components/HotelReservation/EnterDetails/Details/Multiroom/index.tsx
@@ -37,7 +37,7 @@ export default function Details() {
   }))
 
   const {
-    actions: { updateDetails, setIncomplete },
+    actions: { updateDetails, updatePartialGuestData, setIncomplete },
     idx,
     room,
     roomNr,
@@ -93,6 +93,7 @@ export default function Details() {
     formState: { isValid, errors },
     setValue,
     watch,
+    getValues,
   } = methods
 
   const { trackFormSubmit } = useFormTracking(
@@ -114,9 +115,21 @@ export default function Details() {
     if (isValid) {
       handleSubmit(updateDetails)()
     } else {
+      updatePartialGuestData({
+        firstName: getValues("firstName")?.toString(),
+        lastName: getValues("lastName")?.toString(),
+        membershipNo: getValues("membershipNo")?.toString(),
+      })
       setIncomplete()
     }
-  }, [handleSubmit, isValid, setIncomplete, updateDetails])
+  }, [
+    handleSubmit,
+    isValid,
+    setIncomplete,
+    updateDetails,
+    updatePartialGuestData,
+    getValues,
+  ])
 
   useEffect(updateDetailsStore, [updateDetailsStore])
 
diff --git a/apps/scandic-web/components/HotelReservation/EnterDetails/Details/Multiroom/schema.ts b/apps/scandic-web/components/HotelReservation/EnterDetails/Details/Multiroom/schema.ts
index 830513eb1..b0c0dca61 100644
--- a/apps/scandic-web/components/HotelReservation/EnterDetails/Details/Multiroom/schema.ts
+++ b/apps/scandic-web/components/HotelReservation/EnterDetails/Details/Multiroom/schema.ts
@@ -26,8 +26,8 @@ export const multiroomErrors = {
 } as const
 
 export type CrossValidationData = {
-  firstName: string
-  lastName: string
+  firstName: string | undefined
+  lastName: string | undefined
   membershipNo: string | undefined
 }
 
@@ -73,8 +73,8 @@ export function getMultiroomDetailsSchema(
       (data) =>
         !crossValidationData.some(
           (room) =>
-            room.firstName.toLowerCase() === data.firstName.toLowerCase() &&
-            room.lastName.toLowerCase() === data.lastName.toLowerCase()
+            room.firstName?.toLowerCase() === data.firstName.toLowerCase() &&
+            room.lastName?.toLowerCase() === data.lastName.toLowerCase()
         ),
       {
         message: multiroomErrors.FIRST_AND_LAST_NAME_UNIQUE,
@@ -85,8 +85,8 @@ export function getMultiroomDetailsSchema(
       (data) =>
         !crossValidationData.some(
           (room) =>
-            room.firstName.toLowerCase() === data.firstName.toLowerCase() &&
-            room.lastName.toLowerCase() === data.lastName.toLowerCase()
+            room.firstName?.toLowerCase() === data.firstName.toLowerCase() &&
+            room.lastName?.toLowerCase() === data.lastName.toLowerCase()
         ),
       {
         message: multiroomErrors.FIRST_AND_LAST_NAME_UNIQUE,
diff --git a/apps/scandic-web/components/HotelReservation/EnterDetails/Details/RoomOne/index.tsx b/apps/scandic-web/components/HotelReservation/EnterDetails/Details/RoomOne/index.tsx
index d4c81a49f..f504d5e29 100644
--- a/apps/scandic-web/components/HotelReservation/EnterDetails/Details/RoomOne/index.tsx
+++ b/apps/scandic-web/components/HotelReservation/EnterDetails/Details/RoomOne/index.tsx
@@ -43,7 +43,7 @@ export default function Details({ user }: DetailsProps) {
   }))
 
   const {
-    actions: { updateDetails, setIncomplete },
+    actions: { updateDetails, updatePartialGuestData, setIncomplete },
     room,
     roomNr,
     idx,
@@ -89,6 +89,7 @@ export default function Details({ user }: DetailsProps) {
     subscribe,
     setValue,
     watch,
+    getValues,
   } = methods
 
   const { trackFormSubmit } = useFormTracking(
@@ -117,9 +118,21 @@ export default function Details({ user }: DetailsProps) {
     if (formState.isValid) {
       handleSubmit(onSubmit)()
     } else {
+      updatePartialGuestData({
+        firstName: getValues("firstName")?.toString(),
+        lastName: getValues("lastName")?.toString(),
+        membershipNo: getValues("membershipNo")?.toString(),
+      })
       setIncomplete()
     }
-  }, [handleSubmit, formState.isValid, onSubmit, setIncomplete])
+  }, [
+    handleSubmit,
+    formState.isValid,
+    onSubmit,
+    setIncomplete,
+    updatePartialGuestData,
+    getValues,
+  ])
 
   useEffect(updateDetailsStore, [updateDetailsStore])
   const countryCode = watch("countryCode")
diff --git a/apps/scandic-web/stores/enter-details/index.ts b/apps/scandic-web/stores/enter-details/index.ts
index 2467be355..3a434fa79 100644
--- a/apps/scandic-web/stores/enter-details/index.ts
+++ b/apps/scandic-web/stores/enter-details/index.ts
@@ -258,6 +258,21 @@ export function createDetailsStore(
               })
             )
           },
+          updatePartialGuestData(data) {
+            return set(
+              produce((state: DetailsState) => {
+                const currentRoom = state.rooms[idx].room
+
+                //Update only the parts that are relevant for cross-validation
+                if (data.firstName !== undefined)
+                  currentRoom.guest.firstName = data.firstName
+                if (data.lastName !== undefined)
+                  currentRoom.guest.lastName = data.lastName
+                if (data.membershipNo !== undefined)
+                  currentRoom.guest.membershipNo = data.membershipNo
+              })
+            )
+          },
           updateDetails(data) {
             return set(
               produce((state: DetailsState) => {
diff --git a/apps/scandic-web/types/stores/enter-details.ts b/apps/scandic-web/types/stores/enter-details.ts
index aced9125c..80ef9d0b3 100644
--- a/apps/scandic-web/types/stores/enter-details.ts
+++ b/apps/scandic-web/types/stores/enter-details.ts
@@ -17,6 +17,7 @@ import type {
   SignedInDetailsSchema,
 } from "@/types/components/hotelReservation/enterDetails/details"
 import type { StepEnum } from "@/types/enums/step"
+import type { CrossValidationData } from "@/components/HotelReservation/EnterDetails/Details/Multiroom/schema"
 import type { Price } from "../components/hotelReservation/price"
 
 export interface InitialRoomData {
@@ -64,6 +65,7 @@ export interface RoomState {
     updateJoin: (join: boolean) => void
     updatePriceForMembershipNo: (membershipNo: string, isValid: boolean) => void
     updateDetails: (data: DetailsSchema) => void
+    updatePartialGuestData: (data: CrossValidationData) => void
   }
   isComplete: boolean
   room: Room