diff --git a/include/llvm/CodeGen/RegAllocPBQP.h b/include/llvm/CodeGen/RegAllocPBQP.h
index 008a7b3bf3b..7e8745eddef 100644
--- a/include/llvm/CodeGen/RegAllocPBQP.h
+++ b/include/llvm/CodeGen/RegAllocPBQP.h
@@ -22,10 +22,11 @@
 #include "llvm/CodeGen/PBQP/Solution.h"
 
 #include <map>
+#include <set>
 
 namespace llvm {
 
-  class LiveInterval;
+  class LiveIntervals;
   class MachineFunction;
   class MachineLoopInfo;