Index: lib/Target/Mips/Disassembler/MipsDisassembler.cpp
===================================================================
--- lib/Target/Mips/Disassembler/MipsDisassembler.cpp
+++ lib/Target/Mips/Disassembler/MipsDisassembler.cpp
@@ -1919,11 +1919,17 @@
   unsigned RegNum;
 
   unsigned RegLst = fieldFromInstruction(Insn, 21, 5);
+
   // Empty register lists are not allowed.
   if (RegLst == 0)
     return MCDisassembler::Fail;
 
   RegNum = RegLst & 0xf;
+
+  // RegLst values 10-15, and 26-31 are reserved.
+  if (RegNum > 9)
+    return MCDisassembler::Fail;
+
   for (unsigned i = 0; i < RegNum; i++)
     Inst.addOperand(MCOperand::createReg(Regs[i]));
 
Index: test/MC/Disassembler/Mips/micromips32r3/invalid.txt
===================================================================
--- /dev/null
+++ test/MC/Disassembler/Mips/micromips32r3/invalid.txt
@@ -0,0 +1,4 @@
+# RUN: llvm-mc --disassemble %s -triple=mips-unknown-linux -mattr=micromips \
+# RUN:     2>&1 | FileCheck %s
+
+0x21 0xe2 0x5c 0x71 # CHECK: :[[@LINE]]:1: warning: invalid instruction encoding