diff --git a/xo-indentlog/include/xo/indentlog/print/ppdetail_atomic.hpp b/xo-indentlog/include/xo/indentlog/print/ppdetail_atomic.hpp
index 795eae1d..aa1f469a 100644
--- a/xo-indentlog/include/xo/indentlog/print/ppdetail_atomic.hpp
+++ b/xo-indentlog/include/xo/indentlog/print/ppdetail_atomic.hpp
@@ -112,7 +112,10 @@ namespace xo {
 
         PPDETAIL_ATOMIC(bool);
         PPDETAIL_ATOMIC(char);
+#ifdef __APPLE__
+        // unsigned long != std::uint64_t.
         PPDETAIL_ATOMIC(unsigned long);
+#endif
         PPDETAIL_ATOMIC(std::int64_t);
         PPDETAIL_ATOMIC(std::uint64_t);
         PPDETAIL_ATOMIC(std::int32_t);