# Unreal Lightmass executable is outdated **URL:** \ **Category:** Rendering\ **Tags:** building-lighting, unreal-engine, Lightmap\ **Created:** [October 30, 2022, 7:57pm UTC](https://forums.unrealengine.com/t/unreal-lightmass-executable-is-outdated/680381 "2022-10-30T19:57:01Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![eco\_bach2](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@eco\_bach2](https://forums.unrealengine.com/u/eco_bach2)\ **Post date:** [October 30, 2022, 7:57pm UTC](https://forums.unrealengine.com/t/unreal-lightmass-executable-is-outdated/680381/1 "2022-10-30T19:57:01Z")
After doing a custom compile of latest 5.1 preview editor source and trying to build my lighting I get the following warning Warning: Failed to build lighting!!! Unreal Lightmass executable is outdated. Recompile UnrealLightmass project with Development configuration in Visual Studio. Anyone know how to solve? ---
**Author:** ![Dariusz1989](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Dariusz1989](https://forums.unrealengine.com/u/Dariusz1989)\ **Post date:** [November 12, 2022, 8:08pm UTC](https://forums.unrealengine.com/t/unreal-lightmass-executable-is-outdated/680381/2 "2022-11-12T20:08:21Z")
Yo Same issue, did u find a fix? Do this to fix it \> > ```auto ./UnrealEngine_Repo_dir/Engine/Build/BatchFiles/Linux/Build.sh UnrealLightmass Linux Development -verbose ``` use Win64 instead of Linux if u on windows. ---
**Author:** ![MickL](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@MickL](https://forums.unrealengine.com/u/MickL)\ **Post date:** [November 20, 2022, 6:33pm UTC](https://forums.unrealengine.com/t/unreal-lightmass-executable-is-outdated/680381/3 "2022-11-20T18:33:35Z")
Happened for me too after building UE 5.1 for macOS as described in Github Readme. Fix: - Go to UnrealEngine/Engine/Build/BatchFiles/Mac - Exec: ./Build.sh UnrealLightmass Mac Development -verbose ---
**Author:** ![bringfire](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@bringfire](https://forums.unrealengine.com/u/bringfire)\ **Post date:** [December 3, 2022, 9:47pm UTC](https://forums.unrealengine.com/t/unreal-lightmass-executable-is-outdated/680381/4 "2022-12-03T21:47:54Z")
This worked for me: [Debugging lightmass - Gamedev Guide](https://ikrima.dev/ue4guide/graphics-development/lightmass-lightmapping/debugging-lightmass/) ---
**Author:** ![MrHardo1](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@MrHardo1](https://forums.unrealengine.com/u/MrHardo1)\ **Post date:** [December 23, 2022, 9:22pm UTC](https://forums.unrealengine.com/t/unreal-lightmass-executable-is-outdated/680381/5 "2022-12-23T21:22:31Z")
On Windows: - Open Powershell - Navigate to UnrealEngine\Engine\Build\BatchFiles - Enter command " ./Build.bat UnrealLightmass Win64 Development -verbose " Worked for me. ---
**Author:** ![F4r9\_1](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@F4r9\_1](https://forums.unrealengine.com/u/F4r9_1)\ **Post date:** [June 20, 2023, 8:52pm UTC](https://forums.unrealengine.com/t/unreal-lightmass-executable-is-outdated/680381/6 "2023-06-20T20:52:58Z")
Hey there, If you are on Windows 64 bits, do the following to fix the issue: Go to your UnrealEngine folder then Engine\>Build\>BatchFiles then open cmd there and type the following command: Build.bat UnrealLightmass Win64 Development -verbose and wait then try again, it worked for me 🙂 ---
**Author:** ![HermanTheVegan](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@HermanTheVegan](https://forums.unrealengine.com/u/HermanTheVegan)\ **Post date:** [November 26, 2023, 8:54pm UTC](https://forums.unrealengine.com/t/unreal-lightmass-executable-is-outdated/680381/7 "2023-11-26T20:54:41Z")
Thanks, work fine… ---
**Author:** ![HermanTheVegan](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@HermanTheVegan](https://forums.unrealengine.com/u/HermanTheVegan)\ **Post date:** [November 26, 2023, 8:57pm UTC](https://forums.unrealengine.com/t/unreal-lightmass-executable-is-outdated/680381/8 "2023-11-26T20:57:34Z")
For me too, thanks ---
**Author:** ![jfreddy82](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@jfreddy82](https://forums.unrealengine.com/u/jfreddy82)\ **Post date:** [December 7, 2023, 3:13am UTC](https://forums.unrealengine.com/t/unreal-lightmass-executable-is-outdated/680381/9 "2023-12-07T03:13:03Z")
> [@F4r9\_1](#): > > Build.bat UnrealLightmass Win64 Development -verbose thanks ---
**Author:** ![Renanmgs](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Renanmgs](https://forums.unrealengine.com/u/Renanmgs)\ **Post date:** [April 16, 2024, 2:57am UTC](https://forums.unrealengine.com/t/unreal-lightmass-executable-is-outdated/680381/10 "2024-04-16T02:57:55Z")
Nice! ---
**Author:** ![khanh\_ha](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@khanh\_ha](https://forums.unrealengine.com/u/khanh_ha)\ **Post date:** [May 18, 2024, 4:10am UTC](https://forums.unrealengine.com/t/unreal-lightmass-executable-is-outdated/680381/11 "2024-05-18T04:10:55Z")
nice, that works for me too ---
**Author:** ![Ryunawa1](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/ryunawa1/32/690884_2.png) [@Ryunawa1](https://forums.unrealengine.com/u/Ryunawa1)\ **Post date:** [July 11, 2024, 7:52am UTC](https://forums.unrealengine.com/t/unreal-lightmass-executable-is-outdated/680381/12 "2024-07-11T07:52:32Z")
It worked for me too, thanks a lot ! ---
**Author:** ![Skoutyboy](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/skoutyboy/32/876676_2.png) [@Skoutyboy](https://forums.unrealengine.com/u/Skoutyboy)\ **Post date:** [November 13, 2024, 10:45pm UTC](https://forums.unrealengine.com/t/unreal-lightmass-executable-is-outdated/680381/13 "2024-11-13T22:45:37Z")
Thanks! ---
**Author:** ![Slayemin](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Slayemin](https://forums.unrealengine.com/u/Slayemin)\ **Post date:** [April 25, 2025, 10:35pm UTC](https://forums.unrealengine.com/t/unreal-lightmass-executable-is-outdated/680381/14 "2025-04-25T22:35:09Z")
For anyone else stumbling onto this problem with UE 5.x using a source build: The old UE4 workflow was that the UnrealLightmass project was included as a project in your game project source, and you could just build it from your game project. In UE5.x, the UnrealLightmass project is now included exclusively in your UE5 solution. You won’t find it in your project solution. So, just open up the UE5.sln file in visual studio, then in solution explorer, you navigate to “Programs → UnrealLightMass”, right click and “build”. ---
**Author:** ![Magical1](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/magical1/32/914745_2.png) [@Magical1](https://forums.unrealengine.com/u/Magical1)\ **Post date:** [July 15, 2025, 11:59am UTC](https://forums.unrealengine.com/t/unreal-lightmass-executable-is-outdated/680381/15 "2025-07-15T11:59:07Z")
Thanks，it worked for me too ---
**Author:** ![Alexqvqq](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/alexqvqq/32/1189748_2.png) [@Alexqvqq](https://forums.unrealengine.com/u/Alexqvqq)\ **Post date:** [August 8, 2025, 2:32pm UTC](https://forums.unrealengine.com/t/unreal-lightmass-executable-is-outdated/680381/16 "2025-08-08T14:32:06Z")
It work for me bro, Thank YOU!