diff --git a/modules/highgui/src/window_QT.cpp b/modules/highgui/src/window_QT.cpp
index d0eb08dd19..30bf97351f 100755
--- a/modules/highgui/src/window_QT.cpp
+++ b/modules/highgui/src/window_QT.cpp
@@ -49,6 +49,8 @@
 
 #ifdef _WIN32
 #include <windows.h>
+#else
+#include <unistd.h>
 #endif
 
 #ifdef HAVE_QT_OPENGL