diff --git a/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
index 54ca2469fad..74f6b18fd03 100644
--- a/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ b/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -908,6 +908,13 @@ SDNode *PPCDAGToDAGISel::Select(SDNode *N) {
     return nullptr;   // Already selected.
   }
 
+  // In case any misguided DAG-level optimizations form an ADD with a
+  // TargetConstant operand, crash here instead of miscompiling (by selecting
+  // an r+r add instead of some kind of r+i add).
+  if (N->getOpcode() == ISD::ADD &&
+      N->getOperand(1).getOpcode() == ISD::TargetConstant)
+    llvm_unreachable("Invalid ADD with TargetConstant operand");
+
   switch (N->getOpcode()) {
   default: break;