diff --git a/utils/TableGen/DAGISelEmitter.cpp b/utils/TableGen/DAGISelEmitter.cpp
index 18293314263..3f86d2dade3 100644
--- a/utils/TableGen/DAGISelEmitter.cpp
+++ b/utils/TableGen/DAGISelEmitter.cpp
@@ -1957,13 +1957,12 @@ void DAGISelEmitter::EmitInstructionSelector(std::ostream &OS) {
 
   OS << "// The main instruction selector code.\n"
      << "SDNode *SelectCode(SDValue N) {\n"
-     << "  if (N.isMachineOpcode()) {\n"
-     << "    return NULL;   // Already selected.\n"
-     << "  }\n\n"
      << "  MVT::SimpleValueType NVT = N.getNode()->getValueType(0).getSimpleVT();\n"
      << "  switch (N.getOpcode()) {\n"
-     << "  default: break;\n"
-     << "  case ISD::EntryToken:       // These leaves remain the same.\n"
+     << "  default:\n"
+     << "    assert(!N.isMachineOpcode() && \"Node already selected!\");\n"
+     << "    break;\n"
+     << "  case ISD::EntryToken:       // These nodes remain the same.\n"
      << "  case ISD::MEMOPERAND:\n"
      << "  case ISD::BasicBlock:\n"
      << "  case ISD::Register:\n"