diff --git a/src/buffer.c b/src/buffer.c
index a8808d3..94e0b2e 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -66,9 +66,10 @@
  * Return FAIL for failure, OK otherwise.
  */
     int
-open_buffer(read_stdin, eap)
+open_buffer(read_stdin, eap, flags)
     int		read_stdin;	    /* read file from stdin */
     exarg_T	*eap;		    /* for forced 'ff' and 'fenc' or NULL */
+    int		flags;		    /* extra flags for readfile() */
 {
     int		retval = OK;
 #ifdef FEAT_AUTOCMD
@@ -130,7 +131,8 @@
 	netbeansFireChanges = 0;
 #endif
 	retval = readfile(curbuf->b_ffname, curbuf->b_fname,
-		  (linenr_T)0, (linenr_T)0, (linenr_T)MAXLNUM, eap, READ_NEW);
+		  (linenr_T)0, (linenr_T)0, (linenr_T)MAXLNUM, eap,
+		  flags | READ_NEW);
 #ifdef FEAT_NETBEANS_INTG
 	netbeansFireChanges = oldFire;
 #endif
@@ -151,13 +153,15 @@
 	 */
 	curbuf->b_p_bin = TRUE;
 	retval = readfile(NULL, NULL, (linenr_T)0,
-		  (linenr_T)0, (linenr_T)MAXLNUM, NULL, READ_NEW + READ_STDIN);
+		  (linenr_T)0, (linenr_T)MAXLNUM, NULL,
+		  flags | (READ_NEW + READ_STDIN));
 	curbuf->b_p_bin = save_bin;
 	if (retval == OK)
 	{
 	    line_count = curbuf->b_ml.ml_line_count;
 	    retval = readfile(NULL, NULL, (linenr_T)line_count,
-			    (linenr_T)0, (linenr_T)MAXLNUM, eap, READ_BUFFER);
+			    (linenr_T)0, (linenr_T)MAXLNUM, eap,
+			    flags | READ_BUFFER);
 	    if (retval == OK)
 	    {
 		/* Delete the binary lines. */
@@ -412,7 +416,7 @@
     buf->b_nwindows = nwindows;
 #endif
 
-    buf_freeall(buf, del_buf, wipe_buf);
+    buf_freeall(buf, (del_buf ? BFA_DEL : 0) + (wipe_buf ? BFA_WIPE : 0));
 
 #ifdef FEAT_AUTOCMD
     /* Autocommands may have deleted the buffer. */
@@ -511,13 +515,15 @@
 
 /*
  * buf_freeall() - free all things allocated for a buffer that are related to
- * the file.
+ * the file.  flags:
+ * BFA_DEL	  buffer is going to be deleted
+ * BFA_WIPE	  buffer is going to be wiped out
+ * BFA_KEEP_UNDO  do not free undo information
  */
     void
-buf_freeall(buf, del_buf, wipe_buf)
+buf_freeall(buf, flags)
     buf_T	*buf;
-    int		del_buf UNUSED;	    /* buffer is going to be deleted */
-    int		wipe_buf UNUSED;    /* buffer is going to be wiped out */
+    int		flags;
 {
 #ifdef FEAT_AUTOCMD
     int		is_curbuf = (buf == curbuf);
@@ -525,13 +531,13 @@
     apply_autocmds(EVENT_BUFUNLOAD, buf->b_fname, buf->b_fname, FALSE, buf);
     if (!buf_valid(buf))	    /* autocommands may delete the buffer */
 	return;
-    if (del_buf && buf->b_p_bl)
+    if ((flags & BFA_DEL) && buf->b_p_bl)
     {
 	apply_autocmds(EVENT_BUFDELETE, buf->b_fname, buf->b_fname, FALSE, buf);
 	if (!buf_valid(buf))	    /* autocommands may delete the buffer */
 	    return;
     }
-    if (wipe_buf)
+    if (flags & BFA_WIPE)
     {
 	apply_autocmds(EVENT_BUFWIPEOUT, buf->b_fname, buf->b_fname,
 								  FALSE, buf);
@@ -576,10 +582,13 @@
 #ifdef FEAT_TCL
     tcl_buffer_free(buf);
 #endif
-    u_blockfree(buf);		    /* free the memory allocated for undo */
     ml_close(buf, TRUE);	    /* close and delete the memline/memfile */
     buf->b_ml.ml_line_count = 0;    /* no lines in buffer */
-    u_clearall(buf);		    /* reset all undo information */
+    if ((flags & BFA_KEEP_UNDO) == 0)
+    {
+	u_blockfree(buf);	    /* free the memory allocated for undo */
+	u_clearall(buf);	    /* reset all undo information */
+    }
 #ifdef FEAT_SYN_HL
     syntax_clear(&buf->b_s);	    /* reset syntax info */
 #endif
@@ -1423,7 +1432,7 @@
 	    did_filetype = FALSE;
 #endif
 
-	open_buffer(FALSE, NULL);
+	open_buffer(FALSE, NULL, 0);
     }
     else
     {
@@ -1625,7 +1634,7 @@
     if (buf == curbuf)
     {
 	/* free all things allocated for this buffer */
-	buf_freeall(buf, FALSE, FALSE);
+	buf_freeall(buf, 0);
 	if (buf != curbuf)	 /* autocommands deleted the buffer! */
 	    return NULL;
 #if defined(FEAT_AUTOCMD) && defined(FEAT_EVAL)
diff --git a/src/ex_cmds.c b/src/ex_cmds.c
index 602c340..20a39ff 100644
--- a/src/ex_cmds.c
+++ b/src/ex_cmds.c
@@ -3144,6 +3144,7 @@
 #ifdef FEAT_SPELL
     int		did_get_winopts = FALSE;
 #endif
+    int		readfile_flags = 0;
 
     if (eap != NULL)
 	command = eap->do_ecmd_cmd;
@@ -3570,7 +3571,22 @@
 	else
 	    new_name = NULL;
 #endif
-	buf_freeall(curbuf, FALSE, FALSE);   /* free all things for buffer */
+	if (p_ur < 0 || curbuf->b_ml.ml_line_count <= p_ur)
+	{
+	    /* Save all the text, so that the reload can be undone.
+	     * Sync first so that this is a separate undo-able action. */
+	    u_sync(FALSE);
+	    if (u_savecommon(0, curbuf->b_ml.ml_line_count + 1, 0, TRUE)
+								     == FAIL)
+		goto theend;
+	    u_unchanged(curbuf);
+	    buf_freeall(curbuf, BFA_KEEP_UNDO);
+
+	    /* tell readfile() not to clear or reload undo info */
+	    readfile_flags = READ_KEEP_UNDO;
+	}
+	else
+	    buf_freeall(curbuf, 0);   /* free all things for buffer */
 #ifdef FEAT_AUTOCMD
 	/* If autocommands deleted the buffer we were going to re-edit, give
 	 * up and jump to the end. */
@@ -3667,10 +3683,10 @@
 	     * Open the buffer and read the file.
 	     */
 #if defined(FEAT_AUTOCMD) && defined(FEAT_EVAL)
-	    if (should_abort(open_buffer(FALSE, eap)))
+	    if (should_abort(open_buffer(FALSE, eap, readfile_flags)))
 		retval = FAIL;
 #else
-	    (void)open_buffer(FALSE, eap);
+	    (void)open_buffer(FALSE, eap, readfile_flags);
 #endif
 
 #if defined(HAS_SWAP_EXISTS_ACTION)
diff --git a/src/fileio.c b/src/fileio.c
index aa3143e..1c0ac85 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -219,6 +219,7 @@
  * READ_BUFFER	read from curbuf instead of a file (converting after reading
  *		stdin)
  * READ_DUMMY	read into a dummy buffer (to check if file contents changed)
+ * READ_KEEP_UNDO  don't clear undo info or read it from a file
  *
  * return FAIL for failure, OK otherwise
  */
@@ -1195,8 +1196,12 @@
 	conv_restlen = 0;
 #endif
 #ifdef FEAT_PERSISTENT_UNDO
-	read_undo_file = (newfile && curbuf->b_ffname != NULL && curbuf->b_p_udf
-				&& !filtering && !read_stdin && !read_buffer);
+	read_undo_file = (newfile && (flags & READ_KEEP_UNDO) == 0
+				  && curbuf->b_ffname != NULL
+				  && curbuf->b_p_udf
+				  && !filtering
+				  && !read_stdin
+				  && !read_buffer);
 	if (read_undo_file)
 	    sha256_start(&sha_ctx);
 #endif
@@ -7077,6 +7082,7 @@
     buf_T	*savebuf;
     int		saved = OK;
     aco_save_T	aco;
+    int		flags = READ_NEW;
 
     /* set curwin/curbuf for "buf" and save some things */
     aucmd_prepbuf(&aco, buf);
@@ -7089,6 +7095,15 @@
 	old_cursor = curwin->w_cursor;
 	old_topline = curwin->w_topline;
 
+	if (saved == OK && (p_ur < 0 || curbuf->b_ml.ml_line_count <= p_ur))
+	{
+	    /* Save all the text, so that the reload can be undone.
+	     * Sync first so that this is a separate undo-able action. */
+	    u_sync(FALSE);
+	    saved = u_savecommon(0, curbuf->b_ml.ml_line_count + 1, 0, TRUE);
+	    flags |= READ_KEEP_UNDO;
+	}
+
 	/*
 	 * To behave like when a new file is edited (matters for
 	 * BufReadPost autocommands) we first need to delete the current
@@ -7096,7 +7111,7 @@
 	 * the old contents.  Can't use memory only, the file might be
 	 * too big.  Use a hidden buffer to move the buffer contents to.
 	 */
-	if (bufempty())
+	if (bufempty() || saved == FAIL)
 	    savebuf = NULL;
 	else
 	{
@@ -7128,7 +7143,7 @@
 #endif
 	    if (readfile(buf->b_ffname, buf->b_fname, (linenr_T)0,
 			(linenr_T)0,
-			(linenr_T)MAXLNUM, &ea, READ_NEW) == FAIL)
+			(linenr_T)MAXLNUM, &ea, flags) == FAIL)
 	    {
 #if defined(FEAT_AUTOCMD) && defined(FEAT_EVAL)
 		if (!aborting())
@@ -7144,12 +7159,18 @@
 		    (void)move_lines(savebuf, buf);
 		}
 	    }
-	    else if (buf == curbuf)
+	    else if (buf == curbuf)  /* "buf" still valid */
 	    {
 		/* Mark the buffer as unmodified and free undo info. */
 		unchanged(buf, TRUE);
-		u_blockfree(buf);
-		u_clearall(buf);
+		if ((flags & READ_KEEP_UNDO) == 0)
+		{
+		    u_blockfree(buf);
+		    u_clearall(buf);
+		}
+		else
+		    /* Mark all undo states as changed. */
+		    u_unchanged(curbuf);
 	    }
 	}
 	vim_free(ea.cmd);
diff --git a/src/main.c b/src/main.c
index d94b32a..4ccf356 100644
--- a/src/main.c
+++ b/src/main.c
@@ -2470,7 +2470,7 @@
     no_wait_return = TRUE;
     i = msg_didany;
     set_buflisted(TRUE);
-    (void)open_buffer(TRUE, NULL);	/* create memfile and read file */
+    (void)open_buffer(TRUE, NULL, 0);	/* create memfile and read file */
     no_wait_return = FALSE;
     msg_didany = i;
     TIME_MSG("reading stdin");
@@ -2591,7 +2591,9 @@
 		swap_exists_action = SEA_DIALOG;
 #endif
 		set_buflisted(TRUE);
-		(void)open_buffer(FALSE, NULL); /* create memfile, read file */
+
+		/* create memfile, read file */
+		(void)open_buffer(FALSE, NULL, 0);
 
 #if defined(HAS_SWAP_EXISTS_ACTION)
 		if (swap_exists_action == SEA_QUIT)
diff --git a/src/memline.c b/src/memline.c
index 0f7b1d1..9fe9439 100644
--- a/src/memline.c
+++ b/src/memline.c
@@ -2529,7 +2529,7 @@
     int		newfile;	/* flag, see above */
 {
     /* When starting up, we might still need to create the memfile */
-    if (curbuf->b_ml.ml_mfp == NULL && open_buffer(FALSE, NULL) == FAIL)
+    if (curbuf->b_ml.ml_mfp == NULL && open_buffer(FALSE, NULL, 0) == FAIL)
 	return FAIL;
 
     if (curbuf->b_ml.ml_line_lnum != 0)
@@ -3078,7 +3078,7 @@
 	return FAIL;
 
     /* When starting up, we might still need to create the memfile */
-    if (curbuf->b_ml.ml_mfp == NULL && open_buffer(FALSE, NULL) == FAIL)
+    if (curbuf->b_ml.ml_mfp == NULL && open_buffer(FALSE, NULL, 0) == FAIL)
 	return FAIL;
 
     if (copy && (line = vim_strsave(line)) == NULL) /* allocate memory */
diff --git a/src/option.c b/src/option.c
index 8a3f6b5..2c5e88b 100644
--- a/src/option.c
+++ b/src/option.c
@@ -2655,6 +2655,9 @@
 			    (char_u *)100L,
 #endif
 				(char_u *)0L} SCRIPTID_INIT},
+    {"undoreload",  "ur",   P_NUM|P_VI_DEF,
+			    (char_u *)&p_ur, PV_NONE,
+			    { (char_u *)10000L, (char_u *)0L} SCRIPTID_INIT},
     {"updatecount", "uc",   P_NUM|P_VI_DEF,
 			    (char_u *)&p_uc, PV_NONE,
 			    {(char_u *)200L, (char_u *)0L} SCRIPTID_INIT},
diff --git a/src/option.h b/src/option.h
index 5e8574d..78560c6 100644
--- a/src/option.h
+++ b/src/option.h
@@ -826,6 +826,7 @@
 #endif
 EXTERN char_u	*p_udir;	/* 'undodir' */
 EXTERN long	p_ul;		/* 'undolevels' */
+EXTERN long	p_ur;		/* 'undoreload' */
 EXTERN long	p_uc;		/* 'updatecount' */
 EXTERN long	p_ut;		/* 'updatetime' */
 #if defined(FEAT_WINDOWS) || defined(FEAT_FOLDING)
diff --git a/src/proto/buffer.pro b/src/proto/buffer.pro
index a5fe42f..df9c0b4 100644
--- a/src/proto/buffer.pro
+++ b/src/proto/buffer.pro
@@ -1,9 +1,9 @@
 /* buffer.c */
-int open_buffer __ARGS((int read_stdin, exarg_T *eap));
+int open_buffer __ARGS((int read_stdin, exarg_T *eap, int flags));
 int buf_valid __ARGS((buf_T *buf));
 void close_buffer __ARGS((win_T *win, buf_T *buf, int action));
 void buf_clear_file __ARGS((buf_T *buf));
-void buf_freeall __ARGS((buf_T *buf, int del_buf, int wipe_buf));
+void buf_freeall __ARGS((buf_T *buf, int flags));
 void goto_buffer __ARGS((exarg_T *eap, int start, int dir, int count));
 void handle_swap_exists __ARGS((buf_T *old_curbuf));
 char_u *do_bufdel __ARGS((int command, char_u *arg, int addr_count, int start_bnr, int end_bnr, int forceit));
diff --git a/src/proto/undo.pro b/src/proto/undo.pro
index a914c49..2cb149f 100644
--- a/src/proto/undo.pro
+++ b/src/proto/undo.pro
@@ -5,6 +5,7 @@
 int u_inssub __ARGS((linenr_T lnum));
 int u_savedel __ARGS((linenr_T lnum, long nlines));
 int undo_allowed __ARGS((void));
+int u_savecommon __ARGS((linenr_T top, linenr_T bot, linenr_T newbot, int reload));
 void u_compute_hash __ARGS((char_u *hash));
 char_u *u_get_undo_file_name __ARGS((char_u *buf_ffname, int reading));
 void u_write_undo __ARGS((char_u *name, int forceit, buf_T *buf, char_u *hash));
diff --git a/src/undo.c b/src/undo.c
index 58b55ba..6d50cc8 100644
--- a/src/undo.c
+++ b/src/undo.c
@@ -90,7 +90,6 @@
 static void u_unch_branch __ARGS((u_header_T *uhp));
 static u_entry_T *u_get_headentry __ARGS((void));
 static void u_getbot __ARGS((void));
-static int u_savecommon __ARGS((linenr_T, linenr_T, linenr_T));
 static void u_doit __ARGS((int count));
 static void u_undoredo __ARGS((int undo));
 static void u_undo_end __ARGS((int did_undo, int absolute));
@@ -250,7 +249,7 @@
     if (top + 2 == bot)
 	u_saveline((linenr_T)(top + 1));
 
-    return (u_savecommon(top, bot, (linenr_T)0));
+    return (u_savecommon(top, bot, (linenr_T)0, FALSE));
 }
 
 /*
@@ -266,7 +265,7 @@
     if (undo_off)
 	return OK;
 
-    return (u_savecommon(lnum - 1, lnum + 1, lnum + 1));
+    return (u_savecommon(lnum - 1, lnum + 1, lnum + 1, FALSE));
 }
 
 /*
@@ -282,7 +281,7 @@
     if (undo_off)
 	return OK;
 
-    return (u_savecommon(lnum - 1, lnum, lnum + 1));
+    return (u_savecommon(lnum - 1, lnum, lnum + 1, FALSE));
 }
 
 /*
@@ -301,7 +300,7 @@
 	return OK;
 
     return (u_savecommon(lnum - 1, lnum + nlines,
-			nlines == curbuf->b_ml.ml_line_count ? 2 : lnum));
+		     nlines == curbuf->b_ml.ml_line_count ? 2 : lnum, FALSE));
 }
 
 /*
@@ -342,13 +341,16 @@
  * Common code for various ways to save text before a change.
  * "top" is the line above the first changed line.
  * "bot" is the line below the last changed line.
+ * "newbot" is the new bottom line.  Use zero when not known.
+ * "reload" is TRUE when saving for a buffer reload.
  * Careful: may trigger autocommands that reload the buffer.
  * Returns FAIL when lines could not be saved, OK otherwise.
  */
-    static int
-u_savecommon(top, bot, newbot)
+    int
+u_savecommon(top, bot, newbot, reload)
     linenr_T	top, bot;
     linenr_T	newbot;
+    int		reload;
 {
     linenr_T	lnum;
     long	i;
@@ -358,49 +360,53 @@
     u_entry_T	*prev_uep;
     long	size;
 
-    /* When making changes is not allowed return FAIL.  It's a crude way to
-     * make all change commands fail. */
-    if (!undo_allowed())
-	return FAIL;
-
-#ifdef U_DEBUG
-    u_check(FALSE);
-#endif
-#ifdef FEAT_NETBEANS_INTG
-    /*
-     * Netbeans defines areas that cannot be modified.  Bail out here when
-     * trying to change text in a guarded area.
-     */
-    if (netbeans_active())
+    if (!reload)
     {
-	if (netbeans_is_guarded(top, bot))
-	{
-	    EMSG(_(e_guarded));
+	/* When making changes is not allowed return FAIL.  It's a crude way
+	 * to make all change commands fail. */
+	if (!undo_allowed())
 	    return FAIL;
-	}
-	if (curbuf->b_p_ro)
+
+#ifdef FEAT_NETBEANS_INTG
+	/*
+	 * Netbeans defines areas that cannot be modified.  Bail out here when
+	 * trying to change text in a guarded area.
+	 */
+	if (netbeans_active())
 	{
-	    EMSG(_(e_nbreadonly));
-	    return FAIL;
+	    if (netbeans_is_guarded(top, bot))
+	    {
+		EMSG(_(e_guarded));
+		return FAIL;
+	    }
+	    if (curbuf->b_p_ro)
+	    {
+		EMSG(_(e_nbreadonly));
+		return FAIL;
+	    }
 	}
-    }
 #endif
 
 #ifdef FEAT_AUTOCMD
-    /*
-     * Saving text for undo means we are going to make a change.  Give a
-     * warning for a read-only file before making the change, so that the
-     * FileChangedRO event can replace the buffer with a read-write version
-     * (e.g., obtained from a source control system).
-     */
-    change_warning(0);
-    if (bot > curbuf->b_ml.ml_line_count + 1)
-    {
-	/* This happens when the FileChangedRO autocommand changes the file in
-	 * a way it becomes shorter. */
-	EMSG(_("E834: Line count changed unexpectedly"));
-	return FAIL;
+	/*
+	 * Saving text for undo means we are going to make a change.  Give a
+	 * warning for a read-only file before making the change, so that the
+	 * FileChangedRO event can replace the buffer with a read-write version
+	 * (e.g., obtained from a source control system).
+	 */
+	change_warning(0);
+	if (bot > curbuf->b_ml.ml_line_count + 1)
+	{
+	    /* This happens when the FileChangedRO autocommand changes the
+	     * file in a way it becomes shorter. */
+	    EMSG(_("E834: Line count changed unexpectedly"));
+	    return FAIL;
+	}
+#endif
     }
+
+#ifdef U_DEBUG
+    u_check(FALSE);
 #endif
 
     size = bot - top - 1;
@@ -2905,7 +2911,7 @@
 }
 
 /*
- * Called after writing the file and setting b_changed to FALSE.
+ * Called after writing or reloading the file and setting b_changed to FALSE.
  * Now an undo means that the buffer is modified.
  */
     void
@@ -3197,7 +3203,7 @@
 
     /* first save the line for the 'u' command */
     if (u_savecommon(curbuf->b_u_line_lnum - 1,
-				curbuf->b_u_line_lnum + 1, (linenr_T)0) == FAIL)
+		       curbuf->b_u_line_lnum + 1, (linenr_T)0, FALSE) == FAIL)
 	return;
     oldp = u_save_line(curbuf->b_u_line_lnum);
     if (oldp == NULL)
diff --git a/src/vim.h b/src/vim.h
index ce55514..6790a48 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -953,6 +953,7 @@
 #define READ_STDIN	0x04	/* read from stdin */
 #define READ_BUFFER	0x08	/* read from curbuf (converting stdin) */
 #define READ_DUMMY	0x10	/* reading into a dummy buffer */
+#define READ_KEEP_UNDO	0x20	/* keep undo info*/
 
 /* Values for change_indent() */
 #define INDENT_SET	1	/* set indent */
@@ -2174,4 +2175,9 @@
 #define VIF_FORCEIT		4	/* overwrite info already read */
 #define VIF_GET_OLDFILES	8	/* load v:oldfiles */
 
+/* flags for buf_freeall() */
+#define BFA_DEL		1	/* buffer is going to be deleted */
+#define BFA_WIPE	2	/* buffer is going to be wiped out */
+#define BFA_KEEP_UNDO	4	/* do not free undo information */
+
 #endif /* VIM__H */