diff --git a/build/cmake/setup.cmake b/build/cmake/setup.cmake
index a0f6c86188..0bb0815744 100644
--- a/build/cmake/setup.cmake
+++ b/build/cmake/setup.cmake
@@ -71,7 +71,7 @@ if(WXGTK)
     endforeach()
 endif()
 
-set(wxINSTALL_PREFIX ${CMAKE_INSTALL_PREFIX})
+file(TO_CMAKE_PATH "${CMAKE_INSTALL_PREFIX}" wxINSTALL_PREFIX)
 
 check_include_files("stdlib.h;stdarg.h;string.h;float.h" STDC_HEADERS)