Update sn3d.h

sn3d.h

@@ -180,7 +180,7 @@ __attribute__((__format__(__printf__, 1, 2))) inline auto printout(const char *f
 
 #ifdef __cpp_lib_atomic_ref
 #define atomicadd(var, val) \
-  std::atomic_ref<std::remove_reference<decltype(var)>::type>(var).fetch_add(val, std::memory_order_relaxed);
+  std::atomic_ref<typename std::remove_reference<decltype(var)>::type>(var).fetch_add(val, std::memory_order_relaxed);
 #else
 // needed for Apple clang
 #define atomicadd(var, val) __atomic_fetch_add(&var, val, __ATOMIC_RELAXED);