diff --git a/src/Reactor/LLVMReactor.cpp b/src/Reactor/LLVMReactor.cpp
index ccee399..520f1a0 100644
--- a/src/Reactor/LLVMReactor.cpp
+++ b/src/Reactor/LLVMReactor.cpp
@@ -453,7 +453,7 @@
 		case llvm::AtomicOrdering::AcquireRelease: return std::memory_order_acq_rel;
 		case llvm::AtomicOrdering::SequentiallyConsistent: return std::memory_order_seq_cst;
 		default:
-			UNREACHABLE("memoryOrder: %d", memoryOrder);
+			UNREACHABLE("memoryOrder: %d", int(memoryOrder));
 			return std::memory_order_acq_rel;
 		}
 	}