diff --git a/engine/nbproject/build-bullet-natives.xml b/engine/nbproject/build-bullet-natives.xml
index 513e532af..1f4e582a9 100644
--- a/engine/nbproject/build-bullet-natives.xml
+++ b/engine/nbproject/build-bullet-natives.xml
@@ -58,7 +58,7 @@
         <available file="build/bullet-base-mingw/libLinearMath.a" property="haveBulletLibraryMingw"/>
         <available file="build/bullet-base-mingw-64/libLinearMath.a" property="haveBulletLibraryMingw64"/>
         <condition property="doDownloadBulletSource">
-            <not><istrue value="${haveBulletSource}"/></not>
+            <isfalse value="${haveBulletSource}"/>
         </condition>
         <condition property="doBuildMacBase">
             <and>