diff --git a/SDL2pp/RWops.cc b/SDL2pp/RWops.cc
index 108fd6e..0763fc1 100644
--- a/SDL2pp/RWops.cc
+++ b/SDL2pp/RWops.cc
@@ -192,6 +192,7 @@ Sint64 RWops::Size() {
 	Sint64 old_pos = Tell();
 	Sint64 size = Seek(0, SEEK_END);
 	Sint64 back_pos = Seek(old_pos, SEEK_SET);
+	(void)back_pos; // silence unused variable warning on release build
 	assert(back_pos == old_pos);
 	return size;
 }