diff --git a/CMakeLists.txt b/CMakeLists.txt
index 52dfcf0c5d..a49ecd3883 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -17,6 +17,8 @@ if(NOT CMAKE_CONFIGURATION_TYPES)
     endif()
 endif()
 
+file(TO_CMAKE_PATH "${CMAKE_INSTALL_PREFIX}" CMAKE_INSTALL_PREFIX)
+
 # https://blog.kitware.com/cmake-and-the-default-build-type/
 if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
     set(default_build_type "Debug")
diff --git a/build/cmake/setup.cmake b/build/cmake/setup.cmake
index 0bb0815744..cfe2cd17c9 100644
--- a/build/cmake/setup.cmake
+++ b/build/cmake/setup.cmake
@@ -71,7 +71,7 @@ if(WXGTK)
     endforeach()
 endif()
 
-file(TO_CMAKE_PATH "${CMAKE_INSTALL_PREFIX}" wxINSTALL_PREFIX)
+set(wxINSTALL_PREFIX "${CMAKE_INSTALL_PREFIX}")
 
 check_include_files("stdlib.h;stdarg.h;string.h;float.h" STDC_HEADERS)