diff --git a/CMakeLists.txt b/CMakeLists.txt
index 941f32f37..d8c8e755b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -346,11 +346,11 @@ ENDIF()
 IF(WIN32 AND NOT ANDROID)
     OPTION(OSG_DETERMINE_WIN_VERSION "Wheter to automatically determine current Windows version" ON)
 
-	IF(OSG_DETERMINE_WIN_VERSION)
-    # Check window version
-    INCLUDE (OsgDetermineWinVersion)
-    get_WIN32_WINNT(WIN_VERSION)
-    ADD_DEFINITIONS(-D_WIN32_WINNT=${WIN_VERSION})
+    IF(OSG_DETERMINE_WIN_VERSION)
+        # Check window version
+        INCLUDE (OsgDetermineWinVersion)
+        get_WIN32_WINNT(WIN_VERSION)
+        ADD_DEFINITIONS(-D_WIN32_WINNT=${WIN_VERSION})
     ENDIF(OSG_DETERMINE_WIN_VERSION)
 
     IF(MSVC)