diff --git a/CMakeLists.txt b/CMakeLists.txt
index c29e604..6e467be 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -29,10 +29,6 @@ pad_number(VERSION_MINOR 3)
 pad_number(VERSION_REVISION 3)
 set(LIBJPEG_TURBO_VERSION_NUMBER ${VERSION_MAJOR}${VERSION_MINOR}${VERSION_REVISION})
 
-if(NOT WIN32)
-  message(FATAL_ERROR "Platform not supported by this build system.  Use autotools instead.")
-endif()
-
 string(TIMESTAMP BUILD "%Y%m%d")
 
 # This does nothing except when using MinGW.  CMAKE_BUILD_TYPE has no meaning
@@ -166,8 +162,10 @@ endif()
 
 if(64BIT)
   message(STATUS "64-bit build")
+  add_compile_options(-DSIZEOF_SIZE_T=8)
 else()
   message(STATUS "32-bit build")
+  add_compile_options(-DSIZEOF_SIZE_T=4)
 endif()
 
 if(CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
