diff --git a/cmd-new-session.c b/cmd-new-session.c
index 175a3d41..18fffa1b 100644
--- a/cmd-new-session.c
+++ b/cmd-new-session.c
@@ -1,4 +1,4 @@
-/* $Id: cmd-new-session.c,v 1.85 2011-04-06 22:24:00 nicm Exp $ */
+/* $Id: cmd-new-session.c,v 1.86 2011-04-06 22:29:26 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicm@users.sourceforge.net>
@@ -68,9 +68,15 @@ cmd_new_session_exec(struct cmd *self, struct cmd_ctx *ctx)
 	u_int			 sx, sy, i;
 
 	newname = args_get(args, 's');
-	if (newname != NULL && session_find(newname) != NULL) {
-		ctx->error(ctx, "duplicate session: %s", newname);
-		return (-1);
+	if (newname != NULL) {
+		if (!session_check_name(newname)) {
+			ctx->error(ctx, "bad session name: %s", newname);
+			return (-1);
+		}
+		if (session_find(newname) != NULL) {
+			ctx->error(ctx, "duplicate session: %s", newname);
+			return (-1);
+		}
 	}
 
 	target = args_get(args, 't');
diff --git a/cmd-rename-session.c b/cmd-rename-session.c
index af6d8e9c..fd070c77 100644
--- a/cmd-rename-session.c
+++ b/cmd-rename-session.c
@@ -1,4 +1,4 @@
-/* $Id: cmd-rename-session.c,v 1.23 2011-04-06 22:24:01 nicm Exp $ */
+/* $Id: cmd-rename-session.c,v 1.24 2011-04-06 22:29:26 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicm@users.sourceforge.net>
@@ -46,6 +46,10 @@ cmd_rename_session_exec(struct cmd *self, struct cmd_ctx *ctx)
 	const char	*newname;
 
 	newname = args->argv[0];
+	if (!session_check_name(newname)) {
+		ctx->error(ctx, "bad session name: %s", newname);
+		return (-1);
+	}
 	if (session_find(newname) != NULL) {
 		ctx->error(ctx, "duplicate session: %s", newname);
 		return (-1);
diff --git a/cmd.c b/cmd.c
index 70c8e3ad..23458af7 100644
--- a/cmd.c
+++ b/cmd.c
@@ -1,4 +1,4 @@
-/* $Id: cmd.c,v 1.151 2011-04-06 22:24:01 nicm Exp $ */
+/* $Id: cmd.c,v 1.152 2011-04-06 22:29:26 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicm@users.sourceforge.net>
@@ -724,6 +724,12 @@ cmd_find_session(struct cmd_ctx *ctx, const char *arg, int prefer_unattached)
 	if (arglen != 0 && tmparg[arglen - 1] == ':')
 		tmparg[arglen - 1] = '\0';
 
+	/* An empty session name is the current session. */
+	if (*tmparg == '\0') {
+		xfree (tmparg);
+		return (cmd_current_session(ctx, prefer_unattached));
+	}
+
 	/* Find the session, if any. */
 	s = cmd_lookup_session(tmparg, &ambiguous);
 
@@ -839,7 +845,7 @@ no_colon:
 lookup_session:
 	if (ambiguous)
 		goto not_found;
-	if ((s = cmd_lookup_session(arg, &ambiguous)) == NULL)
+	if (*arg != '\0' && (s = cmd_lookup_session(arg, &ambiguous)) == NULL)
 		goto no_session;
 
 	if (sp != NULL)
@@ -980,7 +986,7 @@ no_colon:
 lookup_session:
 	if (ambiguous)
 		goto not_found;
-	if ((s = cmd_lookup_session(arg, &ambiguous)) == NULL)
+	if (*arg != '\0' && (s = cmd_lookup_session(arg, &ambiguous)) == NULL)
 		goto no_session;
 
 	if (sp != NULL)
diff --git a/session.c b/session.c
index 3e92d3d6..3eac8c23 100644
--- a/session.c
+++ b/session.c
@@ -1,4 +1,4 @@
-/* $Id: session.c,v 1.88 2011-02-15 15:09:52 tcunha Exp $ */
+/* $Id: session.c,v 1.89 2011-04-06 22:29:26 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicm@users.sourceforge.net>
@@ -163,6 +163,13 @@ session_destroy(struct session *s)
 	RB_INSERT(sessions, &dead_sessions, s);
 }
 
+/* Check a session name is valid: not empty and no colons. */
+int
+session_check_name(const char *name)
+{
+	return (*name != '\0' && strchr(name, ':') == NULL);
+}
+
 /* Update session active time. */
 void
 session_update_activity(struct session *s)
diff --git a/tmux.h b/tmux.h
index f8152714..9d76f608 100644
--- a/tmux.h
+++ b/tmux.h
@@ -1,4 +1,4 @@
-/* $Id: tmux.h,v 1.617 2011-04-06 22:24:01 nicm Exp $ */
+/* $Id: tmux.h,v 1.618 2011-04-06 22:29:26 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicm@users.sourceforge.net>
@@ -1974,6 +1974,7 @@ struct session	*session_create(const char *, const char *, const char *,
 		     struct environ *, struct termios *, int, u_int, u_int,
 		     char **);
 void		 session_destroy(struct session *);
+int		 session_check_name(const char *);
 void		 session_update_activity(struct session *);
 struct session	*session_next_session(struct session *);
 struct session	*session_previous_session(struct session *);