diff --git a/src/MagnumExternal/Optional/optional.hpp b/src/MagnumExternal/Optional/optional.hpp
index 07db190f5..4891b2572 100644
--- a/src/MagnumExternal/Optional/optional.hpp
+++ b/src/MagnumExternal/Optional/optional.hpp
@@ -154,7 +154,7 @@ template <class T> inline constexpr typename std::remove_reference<T>::type&& co
   # elif defined __clang__ || defined __GNU_LIBRARY__
     __assert(expr, file, line);
   # elif defined __GNUC__
-    _assert(expr, file, line);
+    __assert(expr, file, line);
   # else
   #   error UNSUPPORTED COMPILER
   # endif