diff --git a/SystemTools.cxx b/SystemTools.cxx
index fcd300714d8571ebcf57454d410a2e1ea613d3ae..e72e02d2cce082f26764d1dc0550e5af6c3811d3 100644
--- a/SystemTools.cxx
+++ b/SystemTools.cxx
@@ -744,7 +744,7 @@ void SystemTools::ConvertToUnixSlashes(kwsys_stl::string& path)
   while((pos = path.find('\\', pos)) != kwsys_stl::string::npos)
     {
     // make sure we don't convert an escaped space to a unix slash
-    if(pos < path.size()-2)
+    if(pos < path.size()-1)
       {
       if(path[pos+1] != ' ')
         {