diff --git a/hw/xfree86/os-support/shared/sigio.c b/hw/xfree86/os-support/shared/sigio.c
index e3f0774dc..be78b9eaa 100644
--- a/hw/xfree86/os-support/shared/sigio.c
+++ b/hw/xfree86/os-support/shared/sigio.c
@@ -59,6 +59,8 @@
 #include <errno.h>
 #include <X11/X.h>
 
+#include "os/osdep.h"
+
 #include <xserver_poll.h>
 #include "xf86.h"
 #include "xf86Priv.h"
diff --git a/include/os.h b/include/os.h
index d93e7fe7d..6355fc5e1 100644
--- a/include/os.h
+++ b/include/os.h
@@ -714,7 +714,4 @@ xorg_backtrace(void);
 typedef _sigset_t sigset_t;
 #endif
 
-extern _X_EXPORT int
-xthread_sigmask(int how, const sigset_t *set, sigset_t *oldest);
-
 #endif                          /* OS_H */
diff --git a/os/osdep.h b/os/osdep.h
index 26d430bf1..2999884c4 100644
--- a/os/osdep.h
+++ b/os/osdep.h
@@ -224,4 +224,8 @@ void AutoResetServer(int sig);
 /* clone fd so it gets out of our select mask */
 int os_move_fd(int fd);
 
+/* set signal mask - either on current thread or whole process,
+   depending on whether multithreading is used */
+int xthread_sigmask(int how, const sigset_t *set, sigset_t *oldest);
+
 #endif                          /* _OSDEP_H_ */