diff --git a/include/llvm/Analysis/Dominators.h b/include/llvm/Analysis/Dominators.h
index 778b4eab759..1d7e2f351c7 100644
--- a/include/llvm/Analysis/Dominators.h
+++ b/include/llvm/Analysis/Dominators.h
@@ -322,13 +322,16 @@ public:
   }
   
   /// Return the immediate dominator of A.
-  BasicBlock *getIDom(BasicBlock *A) {
+  BasicBlock *getIDom(BasicBlock *A) const {
+    if (!A) return 0;
+    
     ETNode *NodeA = getNode(A);
     const ETNode *idom = NodeA->getFather();
     return idom ? idom->getData<BasicBlock>() : 0;
   }
   
-  void getChildren(BasicBlock *A, std::vector<BasicBlock*>& children) {
+  void getChildren(BasicBlock *A, std::vector<BasicBlock*>& children) const {
+    if (!A) return;
     ETNode *NodeA = getNode(A);
     const ETNode* son = NodeA->getSon();