diff --git a/Source/cmSourceFile.cxx b/Source/cmSourceFile.cxx
index b833d3fd4..12eb4115b 100644
--- a/Source/cmSourceFile.cxx
+++ b/Source/cmSourceFile.cxx
@@ -24,7 +24,7 @@ cmSourceFile::cmSourceFile(cmMakefile* mf, const std::string& name):
   this->CustomCommand = 0;
   this->Properties.SetCMakeInstance(mf->GetCMakeInstance());
   this->FindFullPathFailed = false;
-  this->IsUiFile = ("ui" ==
+  this->IsUiFile = (".ui" ==
           cmSystemTools::GetFilenameLastExtension(this->Location.GetName()));
 }