diff --git a/Source/cmGeneratorTarget.cxx b/Source/cmGeneratorTarget.cxx
index 9a42ca2ede..14b5a927f5 100644
--- a/Source/cmGeneratorTarget.cxx
+++ b/Source/cmGeneratorTarget.cxx
@@ -519,9 +519,7 @@ bool cmGeneratorTarget::IsSystemIncludeDirectory(const std::string& dir,
     iter = this->SystemIncludesCache.insert(entry).first;
     }
 
-  std::string dirString = dir;
-  return std::binary_search(iter->second.begin(), iter->second.end(),
-                            dirString);
+  return std::binary_search(iter->second.begin(), iter->second.end(), dir);
 }
 
 //----------------------------------------------------------------------------