diff --git a/llvm/lib/Target/AVR/MCTargetDesc/AVRInstPrinter.cpp b/llvm/lib/Target/AVR/MCTargetDesc/AVRInstPrinter.cpp
--- a/llvm/lib/Target/AVR/MCTargetDesc/AVRInstPrinter.cpp
+++ b/llvm/lib/Target/AVR/MCTargetDesc/AVRInstPrinter.cpp
@@ -100,6 +100,16 @@
 
 void AVRInstPrinter::printOperand(const MCInst *MI, unsigned OpNo,
                                   raw_ostream &O) {
+  if (OpNo >= MI->size()) {
+    // Not all operands are correctly disassembled at the moment. This means
+    // that some machine instructions won't have all the necessary operands
+    // set.
+    // To avoid asserting, print <unknown> instead until the necessary support
+    // has been implemented.
+    O << "<unknown>";
+    return;
+  }
+
   const MCOperand &Op = MI->getOperand(OpNo);
   const MCOperandInfo &MOI = this->MII.get(MI->getOpcode()).OpInfo[OpNo];
 
@@ -125,6 +135,16 @@
 /// being encoded as a pc-relative value.
 void AVRInstPrinter::printPCRelImm(const MCInst *MI, unsigned OpNo,
                                    raw_ostream &O) {
+  if (OpNo >= MI->size()) {
+    // Not all operands are correctly disassembled at the moment. This means
+    // that some machine instructions won't have all the necessary operands
+    // set.
+    // To avoid asserting, print <unknown> instead until the necessary support
+    // has been implemented.
+    O << "<unknown>";
+    return;
+  }
+
   const MCOperand &Op = MI->getOperand(OpNo);
 
   if (Op.isImm()) {