diff --git a/src/arch/arm/faults.cc b/src/arch/arm/faults.cc
index 665b2989c8..9cd068f7fa 100644
--- a/src/arch/arm/faults.cc
+++ b/src/arch/arm/faults.cc
@@ -749,15 +749,16 @@ UndefinedInstruction::invoke(ThreadContext *tc, const StaticInstPtr &inst)
 
     // If the mnemonic isn't defined this has to be an unknown instruction.
     assert(unknown || mnemonic != NULL);
+    auto arm_inst = static_cast<ArmStaticInst *>(inst.get());
     if (disabled) {
         panic("Attempted to execute disabled instruction "
-                "'%s' (inst 0x%08x)", mnemonic, machInst);
+                "'%s' (inst 0x%08x)", mnemonic, arm_inst->encoding());
     } else if (unknown) {
         panic("Attempted to execute unknown instruction (inst 0x%08x)",
-              machInst);
+              arm_inst->encoding());
     } else {
         panic("Attempted to execute unimplemented instruction "
-                "'%s' (inst 0x%08x)", mnemonic, machInst);
+                "'%s' (inst 0x%08x)", mnemonic, arm_inst->encoding());
     }
 }
 
diff --git a/src/arch/arm/insts/misc.cc b/src/arch/arm/insts/misc.cc
index 3f29865252..8efb81a6cf 100644
--- a/src/arch/arm/insts/misc.cc
+++ b/src/arch/arm/insts/misc.cc
@@ -324,7 +324,7 @@ RegImmRegShiftOp::generateDisassembly(Addr pc, const SymbolTable *symtab) const
 std::string
 UnknownOp::generateDisassembly(Addr pc, const SymbolTable *symtab) const
 {
-    return csprintf("%-10s (inst %#08x)", "unknown", machInst & mask(32));
+    return csprintf("%-10s (inst %#08x)", "unknown", encoding());
 }
 
 McrMrcMiscInst::McrMrcMiscInst(const char *_mnemonic, ExtMachInst _machInst,
diff --git a/src/arch/arm/insts/misc64.cc b/src/arch/arm/insts/misc64.cc
index 7df2f76ed5..c219bd9ad5 100644
--- a/src/arch/arm/insts/misc64.cc
+++ b/src/arch/arm/insts/misc64.cc
@@ -78,7 +78,7 @@ RegRegRegImmOp64::generateDisassembly(
 std::string
 UnknownOp64::generateDisassembly(Addr pc, const SymbolTable *symtab) const
 {
-    return csprintf("%-10s (inst %#08x)", "unknown", machInst & mask(32));
+    return csprintf("%-10s (inst %#08x)", "unknown", encoding());
 }
 
 Fault