diff --git a/lib/System/CMakeLists.txt b/lib/System/CMakeLists.txt
index 4b9ce5dabf2..5415dd6e300 100644
--- a/lib/System/CMakeLists.txt
+++ b/lib/System/CMakeLists.txt
@@ -1,5 +1,6 @@
 add_llvm_library(LLVMSystem
   Alarm.cpp
+  Atomic.cpp
   Disassembler.cpp
   DynamicLibrary.cpp
   Host.cpp