diff --git a/include/ruby/atomic.h b/include/ruby/atomic.h
index d786df20c9..18072f4810 100644
--- a/include/ruby/atomic.h
+++ b/include/ruby/atomic.h
@@ -72,6 +72,8 @@ typedef unsigned int rb_atomic_t;
 #elif defined(HAVE_GCC_SYNC_BUILTINS)
 typedef unsigned int rb_atomic_t;
 #elif defined(_WIN32)
+# include <winsock2.h>       // to prevent macro redefinitions
+# include <windows.h>        // for `LONG` and `Interlocked` functions
 typedef LONG rb_atomic_t;
 #elif defined(__sun) && defined(HAVE_ATOMIC_H)
 typedef unsigned int rb_atomic_t;