diff --git a/include/empio.h b/include/empio.h
index 5698c721..5ff27835 100644
--- a/include/empio.h
+++ b/include/empio.h
@@ -49,10 +49,10 @@ extern int io_input(struct iop *, int);
 extern int io_inputwaiting(struct iop *);
 extern int io_outputwaiting(struct iop *);
 extern int io_output(struct iop *, int);
+extern int io_output_if_queue_long(struct iop *, int);
 extern int io_peek(struct iop *, char *, int);
 extern int io_read(struct iop *, char *, int);
-extern int io_write(struct iop *, char *, int, int);
-extern int io_output_all(struct iop *);
+extern int io_write(struct iop *, char *, int);
 extern int io_gets(struct iop *, char *, int);
 extern int io_puts(struct iop *, char *);
 extern int io_shutdown(struct iop *, int);
diff --git a/src/lib/empthread/io.c b/src/lib/empthread/io.c
index f2a22704..6679dfc6 100644
--- a/src/lib/empthread/io.c
+++ b/src/lib/empthread/io.c
@@ -54,7 +54,6 @@
 #include "ioqueue.h"
 #include "misc.h"
 #include "queue.h"
-#include "server.h"
 
 struct iop {
     int fd;
@@ -62,6 +61,7 @@ struct iop {
     struct ioqueue *output;
     int flags;
     int bufsize;
+    int last_out;
     struct timeval input_timeout;
 };
 
@@ -94,6 +94,7 @@ io_open(int fd, int flags, int bufsize, struct timeval timeout)
     iop->input = NULL;
     iop->output = NULL;
     iop->flags = flags;
+    iop->last_out = 0;
     iop->bufsize = bufsize;
     iop->input_timeout = timeout;
     if (flags & IO_READ)
@@ -225,9 +226,32 @@ io_output(struct iop *iop, int wait)
     }
 
     ioq_dequeue(iop->output, cc);
+    iop->last_out = ioq_qsize(iop->output);
     return cc;
 }
 
+/*
+ * Write output queued in IOP if enough have been enqueued.
+ * Write if at least one buffer has been filled since the last write.
+ * If WAIT, writing may put the thread to sleep.
+ * Return number of bytes written on success, -1 on error.
+ * In particular, return zero when nothing was written because the
+ * queue was not long, or the write slept and got woken up (only if
+ * WAIT), or the write refused to sleep (only if !WAIT).
+ */
+int
+io_output_if_queue_long(struct iop *iop, int wait)
+{
+    int len = ioq_qsize(iop->output);
+
+    if (CANT_HAPPEN(iop->last_out > len))
+	iop->last_out = 0;
+    if (len - iop->last_out < iop->bufsize)
+	return 0;
+    return io_output(iop, wait);
+}
+
+
 int
 io_peek(struct iop *iop, char *buf, int nbytes)
 {
@@ -250,41 +274,14 @@ io_read(struct iop *iop, char *buf, int nbytes)
 }
 
 int
-io_write(struct iop *iop, char *buf, int nbytes, int wait)
+io_write(struct iop *iop, char *buf, int nbytes)
 {
-    int len;
-
     if ((iop->flags & IO_WRITE) == 0)
 	return -1;
     ioq_append(iop->output, buf, nbytes);
-    len = ioq_qsize(iop->output);
-    if (len > iop->bufsize) {
-	if (wait) {
-	    io_output_all(iop);
-	} else {
-	    /* only try a write every BUFSIZE characters */
-	    if (((len - nbytes) % iop->bufsize) < (len % iop->bufsize))
-		io_output(iop, 0);
-	}
-    }
     return nbytes;
 }
 
-int
-io_output_all(struct iop *iop)
-{
-    int n;
-
-    /*
-     * Mustn't block a player thread while update is pending, or else
-     * a malicous player could delay the update indefinitely
-     */
-    while ((n = io_output(iop, 0)) > 0 && !play_wrlock_wanted)
-	empth_select(iop->fd, EMPTH_FD_WRITE, NULL);
-
-    return n;
-}
-
 int
 io_gets(struct iop *iop, char *buf, int nbytes)
 {
@@ -314,6 +311,7 @@ io_shutdown(struct iop *iop, int flags)
     if (flags & IO_WRITE) {
 	shutdown(iop->fd, 1);
 	ioq_drain(iop->output);
+	iop->last_out = 0;
     }
     return 0;
 }
diff --git a/src/lib/player/recvclient.c b/src/lib/player/recvclient.c
index cd954b2a..74a704ce 100644
--- a/src/lib/player/recvclient.c
+++ b/src/lib/player/recvclient.c
@@ -39,6 +39,7 @@
 #include "journal.h"
 #include "player.h"
 #include "prototypes.h"
+#include "server.h"
 
 /*
  * Receive a line of input from the current player.
@@ -75,8 +76,11 @@ recvclient(char *cmd, int size)
 	    break;
 	}
 
-	/* Make sure player sees prompt */
-	io_output_all(player->iop);
+	/*
+	 * Flush all queued output before potentially sleeping in
+	 * io_input(), to make sure player sees the prompt.
+	 */
+	while (io_output(player->iop, !play_wrlock_wanted) > 0) ;
 
 	/*
 	 * If io_output_all() blocked and got unblocked by command
diff --git a/src/lib/subs/pr.c b/src/lib/subs/pr.c
index 42ae1bc2..01fc13c8 100644
--- a/src/lib/subs/pr.c
+++ b/src/lib/subs/pr.c
@@ -233,9 +233,7 @@ pr_player(struct player *pl, int id, char *buf)
 	p = strchr(bp, '\n');
 	if (p != NULL) {
 	    len = (p - bp) + 1;
-	    io_write(pl->iop, bp, len,
-		     player == pl
-		     && !(pl->command && (pl->command->c_flags & C_MOD)));
+	    io_write(pl->iop, bp, len);
 	    bp += len;
 	    pl->curid = -1;
 	} else {
@@ -243,6 +241,14 @@ pr_player(struct player *pl, int id, char *buf)
 	    bp += len;
 	}
     }
+
+    if (player == pl) {
+	while (io_output_if_queue_long(pl->iop,
+			!play_wrlock_wanted
+			&& !(pl->command && (pl->command->c_flags & C_MOD)))
+	       > 0)
+	    ;
+    }
 }
 
 /*
@@ -286,15 +292,21 @@ upr_player(struct player *pl, int id, char *buf)
 	    }
 	}
 	if (ch == '\n') {
-	    io_write(pl->iop, &ch, 1,
-		     player == pl
-		     && !(pl->command && (pl->command->c_flags & C_MOD)));
+	    io_write(pl->iop, &ch, 1);
 	    pl->curid = -1;
 	} else {
 	    printbuf[0] = ch;
 	    io_puts(pl->iop, printbuf);
 	}
     }
+
+    if (player == pl) {
+	while (io_output_if_queue_long(pl->iop,
+			!play_wrlock_wanted
+			&& !(pl->command && (pl->command->c_flags & C_MOD)))
+	       > 0)
+	    ;
+    }
 }
 
 /*