diff --git a/Source/cmDefinitions.cxx b/Source/cmDefinitions.cxx
index d2b37bb4a0..448ba9d0e9 100644
--- a/Source/cmDefinitions.cxx
+++ b/Source/cmDefinitions.cxx
@@ -58,16 +58,17 @@ void cmDefinitions::Erase(const std::string& key)
 }
 
 //----------------------------------------------------------------------------
-std::set<std::string> cmDefinitions::LocalKeys() const
+std::vector<std::string> cmDefinitions::LocalKeys() const
 {
-  std::set<std::string> keys;
+  std::vector<std::string> keys;
+  keys.reserve(this->Map.size());
   // Consider local definitions.
   for(MapType::const_iterator mi = this->Map.begin();
       mi != this->Map.end(); ++mi)
     {
     if (mi->second.Exists)
       {
-      keys.insert(mi->first);
+      keys.push_back(mi->first);
       }
     }
   return keys;
diff --git a/Source/cmDefinitions.h b/Source/cmDefinitions.h
index 13f885df8b..d21ec23f16 100644
--- a/Source/cmDefinitions.h
+++ b/Source/cmDefinitions.h
@@ -43,7 +43,7 @@ public:
   void Erase(const std::string& key);
 
   /** Get the set of all local keys.  */
-  std::set<std::string> LocalKeys() const;
+  std::vector<std::string> LocalKeys() const;
 
   /** Compute the closure of all defined keys with values.
       This flattens the scope.  The result has no parent.  */
diff --git a/Source/cmMakefile.cxx b/Source/cmMakefile.cxx
index 875442762a..9209e498db 100644
--- a/Source/cmMakefile.cxx
+++ b/Source/cmMakefile.cxx
@@ -89,7 +89,7 @@ public:
       }
   }
 
-  std::set<std::string> LocalKeys() const
+  std::vector<std::string> LocalKeys() const
   {
     return this->VarStack.top().LocalKeys();
   }
@@ -1901,8 +1901,8 @@ void cmMakefile::CheckForUnusedVariables() const
     {
     return;
     }
-  const std::set<std::string>& locals = this->Internal->LocalKeys();
-  std::set<std::string>::const_iterator it = locals.begin();
+  const std::vector<std::string>& locals = this->Internal->LocalKeys();
+  std::vector<std::string>::const_iterator it = locals.begin();
   for (; it != locals.end(); ++it)
     {
     this->CheckForUnused("out of scope", *it);
@@ -4431,10 +4431,10 @@ void cmMakefile::PopScope()
 
   std::set<std::string> init = this->Internal->VarInitStack.top();
   std::set<std::string> usage = this->Internal->VarUsageStack.top();
-  const std::set<std::string>& locals = this->Internal->LocalKeys();
+  const std::vector<std::string>& locals = this->Internal->LocalKeys();
   // Remove initialization and usage information for variables in the local
   // scope.
-  std::set<std::string>::const_iterator it = locals.begin();
+  std::vector<std::string>::const_iterator it = locals.begin();
   for (; it != locals.end(); ++it)
     {
     init.erase(*it);