diff --git a/src/hx/thread/CountingSemaphore.posix.cpp b/src/hx/thread/CountingSemaphore.posix.cpp
index 438c1974a..ed317a776 100644
--- a/src/hx/thread/CountingSemaphore.posix.cpp
+++ b/src/hx/thread/CountingSemaphore.posix.cpp
@@ -2,6 +2,7 @@
 #include <semaphore.h>
 #include <sys/time.h>
 #include <memory>
+#include <cerrno>
 #include <hx/thread/CountingSemaphore.hpp>
 
 struct hx::thread::CountingSemaphore_obj::Impl
@@ -88,4 +89,4 @@ bool hx::thread::CountingSemaphore_obj::tryAcquire(Null<double> timeout)
 			}
 		}
 	}
-}
\ No newline at end of file
+}