diff --git a/Source/cmDefinitions.cxx b/Source/cmDefinitions.cxx
index 2d407189b..34ca68d4a 100644
--- a/Source/cmDefinitions.cxx
+++ b/Source/cmDefinitions.cxx
@@ -84,6 +84,19 @@ const char* cmDefinitions::Set(const char* key, const char* value)
   return def.Exists? def.c_str() : 0;
 }
 
+//----------------------------------------------------------------------------
+std::set<cmStdString> cmDefinitions::LocalKeys() const
+{
+  std::set<cmStdString> keys;
+  // Consider local definitions.
+  for(MapType::const_iterator mi = this->Map.begin();
+      mi != this->Map.end(); ++mi)
+    {
+    keys.insert(mi->first);
+    }
+  return keys;
+}
+
 //----------------------------------------------------------------------------
 cmDefinitions cmDefinitions::Closure() const
 {
diff --git a/Source/cmDefinitions.h b/Source/cmDefinitions.h
index e385e8887..4834d8443 100644
--- a/Source/cmDefinitions.h
+++ b/Source/cmDefinitions.h
@@ -40,6 +40,9 @@ public:
   /** Set (or unset if null) a value associated with a key.  */
   const char* Set(const char* key, const char* value);
 
+  /** Get the set of all local keys.  */
+  std::set<cmStdString> LocalKeys() const;
+
   /** Compute the closure of all defined keys with values.
       This flattens the scope.  The result has no parent.  */
   cmDefinitions Closure() const;