diff --git a/lib/Target/ARM/Disassembler/ARMDisassemblerCore.cpp b/lib/Target/ARM/Disassembler/ARMDisassemblerCore.cpp
index eb9c2cd7a2b..0f3a67db8fa 100644
--- a/lib/Target/ARM/Disassembler/ARMDisassemblerCore.cpp
+++ b/lib/Target/ARM/Disassembler/ARMDisassemblerCore.cpp
@@ -1909,6 +1909,12 @@ static bool DisassembleVFPLdStMulFrm(MCInst &MI, unsigned Opcode, uint32_t insn,
 
   // Next comes the AM5 Opcode.
   ARM_AM::AMSubMode SubMode = getAMSubModeForBits(getPUBits(insn));
+  // Must be either "ia" or "db" submode.
+  if (SubMode != ARM_AM::ia && SubMode != ARM_AM::db) {
+    errs() << "Illegal addressing mode 5 sub-mode!\n";
+    return false;
+  }
+
   unsigned char Imm8 = insn & 0xFF;
   MI.addOperand(MCOperand::CreateImm(ARM_AM::getAM5Opc(SubMode, Imm8)));