diff --git a/lib/Target/PowerPC/PPCISelLowering.cpp b/lib/Target/PowerPC/PPCISelLowering.cpp
index 0f79031..9c2856f 100644
--- a/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -4685,6 +4685,15 @@
                                            SDLoc dl) const {
   assert(Op.getOperand(0).getValueType().isFloatingPoint());
   SDValue Src = Op.getOperand(0);
+
+  // If we have a long double here, it must be that we have an undef of
+  // that type.  In this case return an undef of the target type.
+  if (Src.getValueType() == MVT::ppcf128) {
+    assert(Src.getOpcode() == ISD::UNDEF && "Unhandled ppcf128!");
+    return DAG.getNode(ISD::UNDEF, dl,
+                       Op.getValueType().getSimpleVT().SimpleTy);
+  }
+
   if (Src.getValueType() == MVT::f32)
     Src = DAG.getNode(ISD::FP_EXTEND, dl, MVT::f64, Src);
 
diff --git a/test/CodeGen/PowerPC/pr16556.ll b/test/CodeGen/PowerPC/pr16556.ll
new file mode 100644
index 0000000..dc36f0b
--- /dev/null
+++ b/test/CodeGen/PowerPC/pr16556.ll
@@ -0,0 +1,20 @@
+; RUN: llc < %s
+
+; This test formerly failed due to no handling for a ppc_fp128 undef.
+
+target datalayout = "E-p:32:32:32-S0-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f16:16:16-f32:32:32-f64:64:64-f128:64:128-v64:64:64-v128:128:128-a0:0:64-n32"
+target triple = "powerpc-unknown-linux-gnu"
+
+%core.time.TickDuration.37.125 = type { i64 }
+
+define weak_odr fastcc i64 @_D4core4time12TickDuration30__T2toVAyaa7_7365636f6e6473TlZ2toMxFNaNbNfZl(%core.time.TickDuration.37.125* %.this_arg) {
+entry:
+  br i1 undef, label %noassert, label %assert
+
+assert:                                           ; preds = %entry
+  unreachable
+
+noassert:                                         ; preds = %entry
+  %tmp9 = fptosi ppc_fp128 undef to i64
+  ret i64 %tmp9
+}