diff --git a/llvm/include/llvm/CodeGen/MachineInstr.h b/llvm/include/llvm/CodeGen/MachineInstr.h
--- a/llvm/include/llvm/CodeGen/MachineInstr.h
+++ b/llvm/include/llvm/CodeGen/MachineInstr.h
@@ -120,7 +120,7 @@
 
   // Operands are allocated by an ArrayRecycler.
   MachineOperand *Operands = nullptr;   // Pointer to the first operand.
-  unsigned NumOperands = 0;             // Number of operands on instruction.
+  uint16_t NumOperands = 0;             // Number of operands on instruction.
 
   uint16_t Flags = 0;                   // Various bits of additional
                                         // information about machine
diff --git a/llvm/lib/CodeGen/MachineInstr.cpp b/llvm/lib/CodeGen/MachineInstr.cpp
--- a/llvm/lib/CodeGen/MachineInstr.cpp
+++ b/llvm/lib/CodeGen/MachineInstr.cpp
@@ -192,6 +192,7 @@
 /// an explicit operand it is added at the end of the explicit operand list
 /// (before the first implicit operand).
 void MachineInstr::addOperand(MachineFunction &MF, const MachineOperand &Op) {
+  assert(NumOperands < USHRT_MAX && "Cannot add more operands.");
   assert(MCID && "Cannot add operands before providing an instr descriptor");
 
   // Check if we're adding one of our existing operands.