diff --git a/RosBE-Windows/RosBE.nsi b/RosBE-Windows/RosBE.nsi
index 33fb63b..603b39b 100644
--- a/RosBE-Windows/RosBE.nsi
+++ b/RosBE-Windows/RosBE.nsi
@@ -52,7 +52,15 @@ Function .onInit
     StrCmp $R0 0 +3
         MessageBox MB_OK|MB_ICONEXCLAMATION "The ${PRODUCT_NAME} v${PRODUCT_VERSION} installer is already running."
         Abort
-    StrCpy $INSTDIR "C:\RosBE"
+
+    ${If} $INSTDIR == "" ; InstallDirRegKey not valid?
+        StrCpy $0 $SysDir 1
+        ${If} $0 == "\"
+            StrCpy $0 'C'
+        ${EndIf}
+        StrCpy $INSTDIR "$0:\RosBE"
+    ${EndIf}
+
     Call UninstallPrevious
     !insertmacro INSTALLOPTIONS_EXTRACT "RosSourceDir.ini"
 FunctionEnd