diff --git a/pkg/vere/io/term.c b/pkg/vere/io/term.c
index ca36408854..6ac0b119d3 100644
--- a/pkg/vere/io/term.c
+++ b/pkg/vere/io/term.c
@@ -1038,6 +1038,11 @@ u3_term_get_blew(c3_l tid_l)
   if ( (c3n == u3_Host.ops_u.tem) && uty_u &&
        (c3y == uty_u->wsz_f(uty_u, &col_l, &row_l)) )
   {
+    //  clamp to defaults if ioctl returns zero
+    //  (e.g. Docker PTY with no attached reader)
+    //
+    if ( 0 == col_l ) { col_l = 80; }
+    if ( 0 == row_l ) { row_l = 24; }
     uty_u->tat_u.siz.col_l = col_l;
     uty_u->tat_u.siz.row_l = row_l;
   }