diff --git a/tools/system_libs.py b/tools/system_libs.py
index 36874e986ed47..2832145aabd5c 100644
--- a/tools/system_libs.py
+++ b/tools/system_libs.py
@@ -939,7 +939,7 @@ class libcompiler_rt(MTLibrary, SjLjLibrary):
   # restriction soon: https://reviews.llvm.org/D71738
   force_object_files = True
 
-  cflags = ['-fno-builtin', '-DNDEBUG', '-DCOMPILER_RT_HAS_UNAME=1']
+  cflags = ['-fno-builtin', '-DNDEBUG', '-DCOMPILER_RT_HAS_UNAME=1', '-DCOMPILER_RT_HAS_ATOMICS=1']
   src_dir = 'system/lib/compiler-rt/lib/builtins'
   profile_src_dir = 'system/lib/compiler-rt/lib/profile'
   includes = ['system/lib/libc', 'system/lib/compiler-rt/include']