diff --git a/test/meson.build b/test/meson.build
index 457dfe41..b9aa1168 100644
--- a/test/meson.build
+++ b/test/meson.build
@@ -23,6 +23,7 @@ elif libui_OS == 'darwin'
 else
 	libui_test_sources += [
 		'controls_unix.c',
+		'controls_unix_errors.cpp',
 	]
 endif
 
diff --git a/test/test_unix.h b/test/test_unix.h
new file mode 100644
index 00000000..e2876e35
--- /dev/null
+++ b/test/test_unix.h
@@ -0,0 +1,3 @@
+// 10 june 2019
+#define libuiOSHeader "../ui_unix.h"
+#include "test.h"
diff --git a/ui_unix.h b/ui_unix.h
index 8975c4cb..b7f0ccdf 100644
--- a/ui_unix.h
+++ b/ui_unix.h
@@ -11,6 +11,10 @@ This file assumes that you have included <gtk/gtk.h> and "ui.h" beforehand. It p
 extern "C" {
 #endif
 
+struct uiControlOSVtable {
+	size_t Size;
+};
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/unix/controls.c b/unix/controls.c
new file mode 100644
index 00000000..b0ff2c98
--- /dev/null
+++ b/unix/controls.c
@@ -0,0 +1,20 @@
+// 8 june 2019
+#include "uipriv_unix.h"
+
+bool uiprivOSVtableValid(const uiControlOSVtable *osVtable, const char *func)
+{
+	if (osVtable->Size != sizeof (uiControlOSVtable)) {
+		uiprivProgrammerErrorWrongStructSize(osVtable->Size, "uiControlOSVtable", func);
+		return false;
+	}
+	return true;
+}
+
+uiControlOSVtable *uiprivCloneOSVtable(const uiControlOSVtable *osVtable)
+{
+	uiControlOSVtable *v2;
+
+	v2 = uiprivNew(uiControlOSVtable);
+	*v2 = *osVtable;
+	return v2;
+}
diff --git a/unix/meson.build b/unix/meson.build
index 3ba81095..f8a35ded 100644
--- a/unix/meson.build
+++ b/unix/meson.build
@@ -1,6 +1,7 @@
 # 23 march 2019
 
 libui_sources += [
+	'unix/controls.c',
 	'unix/main.c',
 ]