diff --git a/src/os_mswin.c b/src/os_mswin.c
index 448b2bf..256da04 100644
--- a/src/os_mswin.c
+++ b/src/os_mswin.c
@@ -1971,6 +1971,10 @@
 # define VIM_CLASSNAME      "VIM_MESSAGES"
 # define VIM_CLASSNAME_LEN  (sizeof(VIM_CLASSNAME) - 1)
 
+// Timeout for sending a message to another Vim instance.  Normally this works
+// instantly, but it may hang when the other Vim instance is halted.
+# define SENDMESSAGE_TIMEOUT	(5 * 1000)
+
 // Communication is via WM_COPYDATA messages. The message type is sent in
 // the dwData parameter. Types are defined here.
 # define COPYDATA_KEYS		0
@@ -1992,9 +1996,9 @@
 
 /*
  * Tell the other side what encoding we are using.
- * Errors are ignored.
+ * Return -1 if timeout happens.  Other errors are ignored.
  */
-    static void
+    static int
 serverSendEnc(HWND target)
 {
     COPYDATASTRUCT data;
@@ -2002,8 +2006,11 @@
     data.dwData = COPYDATA_ENCODING;
     data.cbData = (DWORD)STRLEN(p_enc) + 1;
     data.lpData = p_enc;
-    (void)SendMessage(target, WM_COPYDATA, (WPARAM)message_window,
-							     (LPARAM)(&data));
+    if (SendMessageTimeout(target, WM_COPYDATA,
+	    (WPARAM)message_window, (LPARAM)&data,
+	    SMTO_ABORTIFHUNG, SENDMESSAGE_TIMEOUT, NULL) == 0)
+	return -1;
+    return 0;
 }
 
 /*
@@ -2061,6 +2068,7 @@
 	COPYDATASTRUCT	reply;
 	char_u		*res;
 	int		retval;
+	DWORD_PTR	dwret = 0;
 	char_u		*str;
 	char_u		*tofree;
 
@@ -2114,9 +2122,17 @@
 	    reply.lpData = res;
 	    reply.cbData = (DWORD)STRLEN(res) + 1;
 
-	    serverSendEnc(sender);
-	    retval = (int)SendMessage(sender, WM_COPYDATA,
-				    (WPARAM)message_window, (LPARAM)(&reply));
+	    if (serverSendEnc(sender) < 0)
+		retval = -1;
+	    else
+	    {
+		if (SendMessageTimeout(sender, WM_COPYDATA,
+			(WPARAM)message_window, (LPARAM)&reply,
+			SMTO_ABORTIFHUNG, SENDMESSAGE_TIMEOUT, &dwret) == 0)
+		    retval = -1;
+		else
+		    retval = (int)dwret;
+	    }
 	    vim_free(tofree);
 	    vim_free(res);
 	    return retval;
@@ -2394,6 +2410,7 @@
     HWND	target;
     COPYDATASTRUCT data;
     long_u	n = 0;
+    DWORD_PTR	dwret = 0;
 
     // The "name" argument is a magic cookie obtained from expand("<client>").
     // It should be of the form 0xXXXXX - i.e. a C hex literal, which is the
@@ -2410,12 +2427,13 @@
     data.cbData = (DWORD)STRLEN(reply) + 1;
     data.lpData = reply;
 
-    serverSendEnc(target);
-    if (SendMessage(target, WM_COPYDATA, (WPARAM)message_window,
-							     (LPARAM)(&data)))
-	return 0;
-
-    return -1;
+    if (serverSendEnc(target) < 0)
+	return -1;
+    if (SendMessageTimeout(target, WM_COPYDATA,
+		(WPARAM)message_window, (LPARAM)&data,
+		SMTO_ABORTIFHUNG, SENDMESSAGE_TIMEOUT, &dwret) == 0)
+	return -1;
+    return dwret ? 0 : -1;
 }
 
     int
@@ -2432,6 +2450,7 @@
     COPYDATASTRUCT data;
     char_u	*retval = NULL;
     int		retcode = 0;
+    DWORD_PTR	dwret = 0;
     char_u	altname_buf[MAX_PATH];
 
     // Execute locally if no display or target is ourselves
@@ -2463,9 +2482,13 @@
     data.cbData = (DWORD)STRLEN(cmd) + 1;
     data.lpData = cmd;
 
-    serverSendEnc(target);
-    if (SendMessage(target, WM_COPYDATA, (WPARAM)message_window,
-							(LPARAM)(&data)) == 0)
+    if (serverSendEnc(target) < 0)
+	return -1;
+    if (SendMessageTimeout(target, WM_COPYDATA,
+		(WPARAM)message_window, (LPARAM)&data,
+		SMTO_ABORTIFHUNG, SENDMESSAGE_TIMEOUT, &dwret) == 0)
+	return -1;
+    if (dwret == 0)
 	return -1;
 
     if (asExpr)