2 files changed, 17 insertions, 1 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index cb5d3bacba5..8b4029bd7b3 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,8 @@
+2011-07-02  Chong Yidong  <cyd@stupidchicken.com>
+
+        * keyboard.c (command_loop_1): If a down-mouse event is unbound,
+        leave any prefix arg for the up event (Bug#1586).
+
 2011-07-02  Lars Magne Ingebrigtsen  <larsi@gnus.org>
 
         * lread.c (syms_of_lread): Mention single symbols defined by
diff --git a/src/keyboard.c b/src/keyboard.c
index 3441f1dfd12..16300e6154c 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -1539,7 +1539,18 @@ command_loop_1 (void)
           message_with_string ("%s is undefined", keys, 0);
           KVAR (current_kboard, defining_kbd_macro) = Qnil;
           update_mode_lines = 1;
-          KVAR (current_kboard, Vprefix_arg) = Qnil;
+          /* If this is a down-mouse event, don't reset prefix-arg;
+             pass it to the command run by the up event.  */
+          if (EVENT_HAS_PARAMETERS (last_command_event))
+            {
+              Lisp_Object breakdown
+                = parse_modifiers (EVENT_HEAD (last_command_event));
+              int modifiers = XINT (XCAR (XCDR (breakdown)));
+              if (!(modifiers & down_modifier))
+                KVAR (current_kboard, Vprefix_arg) = Qnil;
+            }
+          else
+            KVAR (current_kboard, Vprefix_arg) = Qnil;
         }
       else
         {