diff --git a/lib/Target/ARM/Disassembler/ARMDisassembler.cpp b/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
index d1eb5b3004b..4e9c3e58a5f 100644
--- a/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
+++ b/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
@@ -1004,10 +1004,9 @@ static DecodeStatus DecodeBitfieldMaskOperand(llvm::MCInst &Inst, unsigned Val,
   unsigned msb = fieldFromInstruction32(Val, 5, 5);
   unsigned lsb = fieldFromInstruction32(Val, 0, 5);
 
-  uint32_t msb_mask = (1 << (msb+1)) - 1;
-  if (msb == 31) msb_mask = 0xFFFFFFFF;
-  uint32_t lsb_mask = (1 << lsb) - 1;
-  if (lsb == 31) lsb_mask = 0xFFFFFFFF;
+  uint32_t msb_mask = 0xFFFFFFFF;
+  if (msb != 31) msb_mask = (1U << (msb+1)) - 1;
+  uint32_t lsb_mask = (1U << lsb) - 1;
 
   Inst.addOperand(MCOperand::CreateImm(~(msb_mask ^ lsb_mask)));
   return MCDisassembler::Success;