diff --git a/compiler-rt/lib/builtins/atomic.c b/compiler-rt/lib/builtins/atomic.c
--- a/compiler-rt/lib/builtins/atomic.c
+++ b/compiler-rt/lib/builtins/atomic.c
@@ -52,7 +52,7 @@
 // defined.  Each platform should define the Lock type, and corresponding
 // lock() and unlock() functions.
 ////////////////////////////////////////////////////////////////////////////////
-#ifdef __FreeBSD__
+#if defined(__FreeBSD__) || defined(__DragonFly__)
 #include <errno.h>
 // clang-format off
 #include <sys/types.h>