diff --git a/Util/CMake/SetAMReXOptions.cmake b/Util/CMake/SetAMReXOptions.cmake
index ed8432f..34b92ca 100644
--- a/Util/CMake/SetAMReXOptions.cmake
+++ b/Util/CMake/SetAMReXOptions.cmake
@@ -27,9 +27,11 @@ set(AMReX_HDF5 ${OPTION_ENABLE_HDF5})
 
 if(OPTION_CUDA)
   set(AMReX_GPU_BACKEND CUDA CACHE STRING "AMReX GPU type" FORCE)
+  set(AMReX_GPU_MAX_THREADS 256 CACHE STRING "Max threads to use" FORCE)
 elseif(OPTION_HIP)
   set(AMReX_GPU_BACKEND HIP CACHE STRING "AMReX GPU type" FORCE)
   set(AMReX_AMD_ARCH ${AMD_ARCH} CACHE STRING "AMD GPU ARCH" FORCE)
+  set(AMReX_GPU_MAX_THREADS 256 CACHE STRING "Max threads to use" FORCE)
 elseif(OPTION_SYCL)
   set(AMReX_GPU_BACKEND SYCL CACHE STRING "AMReX GPU type" FORCE)
 else()