diff --git a/src/ex_cmds.h b/src/ex_cmds.h
--- a/src/ex_cmds.h
+++ b/src/ex_cmds.h
@@ -788,7 +788,7 @@
 EX(CMD_rubyfile,	"rubyfile",	ex_rubyfile,
 			RANGE|FILE1|NEEDARG|CMDWIN),
 EX(CMD_rundo,		"rundo",	ex_rundo,
-			NEEDARG|EXTRA|XFILE),
+			BANG|NEEDARG|EXTRA|XFILE),
 EX(CMD_rviminfo,	"rviminfo",	ex_viminfo,
 			BANG|FILE1|TRLBAR|CMDWIN),
 EX(CMD_substitute,	"substitute",	do_sub,
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -8551,7 +8551,7 @@
     char_u hash[UNDO_HASH_SIZE];
 
     u_compute_hash(hash);
-    u_read_undo(eap->arg, hash, NULL);
+    u_read_undo(eap->arg, hash, NULL, eap->forceit);
 }
 #endif
 
diff --git a/src/fileio.c b/src/fileio.c
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -2616,7 +2616,7 @@
 	char_u	hash[UNDO_HASH_SIZE];
 
 	sha256_finish(&sha_ctx, hash);
-	u_read_undo(NULL, hash, fname);
+	u_read_undo(NULL, hash, fname, FALSE);
     }
 #endif
 
diff --git a/src/proto/undo.pro b/src/proto/undo.pro
--- a/src/proto/undo.pro
+++ b/src/proto/undo.pro
@@ -9,7 +9,7 @@
 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));
-void u_read_undo __ARGS((char_u *name, char_u *hash, char_u *orig_name));
+void u_read_undo __ARGS((char_u *name, char_u *hash, char_u *orig_name, int force));
 void u_undo __ARGS((int count));
 void u_redo __ARGS((int count));
 void undo_time __ARGS((long step, int sec, int file, int absolute));
diff --git a/src/undo.c b/src/undo.c
--- a/src/undo.c
+++ b/src/undo.c
@@ -1555,10 +1555,11 @@
  * "hash[UNDO_HASH_SIZE]" must be the hash value of the buffer text.
  */
     void
-u_read_undo(name, hash, orig_name)
+u_read_undo(name, hash, orig_name, force)
     char_u *name;
     char_u *hash;
     char_u *orig_name;
+    int    force; /* :rundo! */
 {
     char_u	*file_name;
     FILE	*fp;
@@ -1675,8 +1676,9 @@
 	goto error;
     }
     line_count = (linenr_T)get4c(fp);
-    if (memcmp(hash, read_hash, UNDO_HASH_SIZE) != 0
+    if ((memcmp(hash, read_hash, UNDO_HASH_SIZE) != 0
 				  || line_count != curbuf->b_ml.ml_line_count)
+				  && !force)
     {
 	if (p_verbose > 0 || name != NULL)
 	{