diff --git a/src/convexos.h b/src/convexos.h
new file mode 100644
index 00000000000..94cdbf68346
--- /dev/null
+++ b/src/convexos.h
@@ -0,0 +1,10 @@
+/* Definitions file for GNU Emacs running on ConvexOS.  */
+
+#include "bsd4-3.h"
+
+/* First pty name is /dev/pty?0.  We have to search for it. */
+#undef FIRST_PTY_LETTER
+#define FIRST_PTY_LETTER first_pty_letter
+
+/* getpgrp requires no arguments. */
+#define GETPGRP_NO_ARG