diff --git a/lib/VMCore/AsmWriter.cpp b/lib/VMCore/AsmWriter.cpp
index b109cb006eb..f70a82839aa 100644
--- a/lib/VMCore/AsmWriter.cpp
+++ b/lib/VMCore/AsmWriter.cpp
@@ -744,6 +744,7 @@ std::ostream &AssemblyWriter::printTypeAtLeastOneLevel(const Type *Ty) {
 
 void AssemblyWriter::writeOperand(const Value *Operand, bool PrintType, 
                                   bool PrintName) {
+  assert(Operand != 0 && "Illegal Operand");
   if (PrintType) { Out << ' '; printType(Operand->getType()); }
   WriteAsOperandInternal(Out, Operand, PrintName, TypeNames, &Machine);
 }