diff --git a/src/arch/riscv/insts/standard.cc b/src/arch/riscv/insts/standard.cc
index bcf0741..60cf4fc 100644
--- a/src/arch/riscv/insts/standard.cc
+++ b/src/arch/riscv/insts/standard.cc
@@ -60,7 +60,11 @@
     ss << mnemonic << ' ' << registerName(_destRegIdx[0]) << ", ";
     if (_numSrcRegs > 0)
         ss << registerName(_srcRegIdx[0]) << ", ";
-    ss << MiscRegNames.at(csr);
+    auto name = MiscRegNames.find(csr);
+    if (name != MiscRegNames.end())
+        ss << name->second;
+    else
+        ss << "?? (" << hex << "0x" << csr << ")";
     return ss.str();
 }