diff --git a/utils/build_script_windows.bat b/utils/build_script_windows.bat
index d1104328..96f04148 100644
--- a/utils/build_script_windows.bat
+++ b/utils/build_script_windows.bat
@@ -8,7 +8,7 @@ SET LOCAL_BOOST_LIB_PATH=C:\dev\_sdk\boost_1_68_0\lib64-msvc-14.1
 SET MY_PATH=%~dp0
 SET SOURCES_PATH=%MY_PATH:~0,-7%
 
-IF [%build_prefix%] == [] (
+IF NOT [%build_prefix%] == [] (
   SET ACHIVE_NAME_PREFIX=%ACHIVE_NAME_PREFIX%%build_prefix%-
 )