diff --git a/lib/Target/X86/X86ISelPattern.cpp b/lib/Target/X86/X86ISelPattern.cpp
index 5d91fe41b48..0e77a7f8b8e 100644
--- a/lib/Target/X86/X86ISelPattern.cpp
+++ b/lib/Target/X86/X86ISelPattern.cpp
@@ -1384,6 +1384,14 @@ unsigned ISel::SelectExpr(SDOperand N) {
     }
     BuildMI(BB, Opc, 1,Result).addImm(cast<ConstantSDNode>(N)->getValue());
     return Result;
+  case ISD::UNDEF:
+    if (Node->getValueType(0) == MVT::f64) {
+      // FIXME: SHOULD TEACH STACKIFIER ABOUT UNDEF VALUES!
+      BuildMI(BB, X86::FLD0, 0, Result);
+    } else {
+      BuildMI(BB, X86::IMPLICIT_DEF, 0, Result);
+    }
+    return Result;
   case ISD::GlobalAddress: {
     GlobalValue *GV = cast<GlobalAddressSDNode>(N)->getGlobal();
     BuildMI(BB, X86::MOV32ri, 1, Result).addGlobalAddress(GV);