diff --git a/libaegisub/unix/util.cpp b/libaegisub/unix/util.cpp
index 4cf67211983fabace6b8310baa679844c6416577..01343a46d7f3f7fd719fd016e53827171cfe682d 100644
--- a/libaegisub/unix/util.cpp
+++ b/libaegisub/unix/util.cpp
@@ -26,7 +26,7 @@ namespace agi { namespace util {
 void SetThreadName(const char *) { }
 
 void sleep_for(int ms) {
-#ifdef __clang__
+#ifdef _LIBCPP_VERSION
 	std::this_thread::sleep_for(std::chrono::milliseconds(ms));
 #else
 	boost::this_thread::sleep_for(boost::chrono::milliseconds(ms));