diff --git a/lib/Target/X86/X86RegisterInfo.cpp b/lib/Target/X86/X86RegisterInfo.cpp
index 43057c0fdf6..ccbe579a468 100644
--- a/lib/Target/X86/X86RegisterInfo.cpp
+++ b/lib/Target/X86/X86RegisterInfo.cpp
@@ -237,6 +237,7 @@ X86RegisterInfo::getCalleeSavedRegs(const MachineFunction *MF) const {
   bool HasAVX = TM.getSubtarget<X86Subtarget>().hasAVX();
   bool HasAVX512 = TM.getSubtarget<X86Subtarget>().hasAVX512();
 
+  assert(MF && "MachineFunction required");
   switch (MF->getFunction()->getCallingConv()) {
   case CallingConv::GHC:
   case CallingConv::HiPE:
diff --git a/lib/Target/X86/X86RegisterInfo.h b/lib/Target/X86/X86RegisterInfo.h
index 3ee328f2e59..447ff953da8 100644
--- a/lib/Target/X86/X86RegisterInfo.h
+++ b/lib/Target/X86/X86RegisterInfo.h
@@ -101,7 +101,7 @@ public:
   /// getCalleeSavedRegs - Return a null-terminated list of all of the
   /// callee-save registers on this target.
   const uint16_t *
-  getCalleeSavedRegs(const MachineFunction* MF = 0) const override;
+  getCalleeSavedRegs(const MachineFunction* MF) const override;
   const uint32_t *getCallPreservedMask(CallingConv::ID) const override;
   const uint32_t *getNoPreservedMask() const;