diff --git a/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp b/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
--- a/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
@@ -1505,8 +1505,8 @@
   // the blocks in the same order. This will help identical PHIs be eliminated
   // by other passes. Other passes shouldn't depend on this for correctness
   // however.
-  PHINode *FirstPN = cast<PHINode>(PN.getParent()->begin());
-  if (&PN != FirstPN)
+  PHINode *FirstPN = dyn_cast<PHINode>(PN.getParent()->begin());
+  if (FirstPN && &PN != FirstPN)
     for (unsigned I = 0, E = FirstPN->getNumIncomingValues(); I != E; ++I) {
       BasicBlock *BBA = PN.getIncomingBlock(I);
       BasicBlock *BBB = FirstPN->getIncomingBlock(I);