diff --git a/llvm/include/llvm/CodeGen/MachineBasicBlock.h b/llvm/include/llvm/CodeGen/MachineBasicBlock.h
index 62394cfc9096..b3578584e633 100644
--- a/llvm/include/llvm/CodeGen/MachineBasicBlock.h
+++ b/llvm/include/llvm/CodeGen/MachineBasicBlock.h
@@ -217,12 +217,7 @@ public:
   
   /// isSuccessor - Return true if the specified MBB is a successor of this
   /// block.
-  bool isSuccessor(MachineBasicBlock *MBB) const {
-    for (const_succ_iterator I = succ_begin(), E = succ_end(); I != E; ++I)
-      if (*I == MBB)
-        return true;
-    return false;
-  }
+  bool isSuccessor(MachineBasicBlock *MBB) const;
 
   /// getFirstTerminator - returns an iterator to the first terminator
   /// instruction of this basic block. If a terminator does not exist,
diff --git a/llvm/lib/CodeGen/MachineBasicBlock.cpp b/llvm/lib/CodeGen/MachineBasicBlock.cpp
index 39780350dedf..44f7f90a65b1 100644
--- a/llvm/lib/CodeGen/MachineBasicBlock.cpp
+++ b/llvm/lib/CodeGen/MachineBasicBlock.cpp
@@ -192,3 +192,9 @@ void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) {
   assert(I != Predecessors.end() && "Pred is not a predecessor of this block!");
   Predecessors.erase(I);
 }
+
+bool MachineBasicBlock::isSuccessor(MachineBasicBlock *MBB) const {
+  std::vector<MachineBasicBlock *>::const_iterator I =
+    std::find(Successors.begin(), Successors.end(), MBB);
+  return I != Successors.end();
+}