diff --git a/sysdeps/unix/bsd/sun/sunos4/tcflow.c b/sysdeps/unix/bsd/sun/sunos4/tcflow.c
index 5accafd47c..bb9a7fc7a0 100644
--- a/sysdeps/unix/bsd/sun/sunos4/tcflow.c
+++ b/sysdeps/unix/bsd/sun/sunos4/tcflow.c
@@ -19,6 +19,7 @@ Cambridge, MA 02139, USA.  */
 #include <ansidecl.h>
 #include <errno.h>
 #include <termios.h>
+#include <sys/ioctl.h>
 
 /* Suspend or restart transmission on FD.  */
 int