diff --git a/modules/util/truncate.go b/modules/util/truncate.go
new file mode 100644
index 0000000000..8d0f630973
--- /dev/null
+++ b/modules/util/truncate.go
@@ -0,0 +1,35 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package util
+
+import "unicode/utf8"
+
+// SplitStringAtByteN splits a string at byte n accounting for rune boundaries. (Combining characters are not accounted for.)
+func SplitStringAtByteN(input string, n int) (left, right string) {
+	if len(input) <= n {
+		left = input
+		return
+	}
+
+	if !utf8.ValidString(input) {
+		left = input[:n-3] + "..."
+		right = "..." + input[n-3:]
+		return
+	}
+
+	// in UTF8 "…" is 3 bytes so doesn't really gain us anything...
+	end := 0
+	for end <= n-3 {
+		_, size := utf8.DecodeRuneInString(input[end:])
+		if end+size > n-3 {
+			break
+		}
+		end += size
+	}
+
+	left = input[:end] + "…"
+	right = "…" + input[end:]
+	return
+}
diff --git a/routers/web/repo/compare.go b/routers/web/repo/compare.go
index fddfc4a63a..e66aa614cb 100644
--- a/routers/web/repo/compare.go
+++ b/routers/web/repo/compare.go
@@ -24,6 +24,7 @@ import (
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/upload"
+	"code.gitea.io/gitea/modules/util"
 	"code.gitea.io/gitea/services/gitdiff"
 )
 
@@ -567,6 +568,18 @@ func PrepareCompareDiff(
 	} else {
 		title = headBranch
 	}
+	if len(title) > 255 {
+		var trailer string
+		title, trailer = util.SplitStringAtByteN(title, 255)
+		if len(trailer) > 0 {
+			if ctx.Data["content"] != nil {
+				ctx.Data["content"] = fmt.Sprintf("%s\n\n%s", trailer, ctx.Data["content"])
+			} else {
+				ctx.Data["content"] = trailer + "\n"
+			}
+		}
+	}
+
 	ctx.Data["title"] = title
 	ctx.Data["Username"] = headUser.Name
 	ctx.Data["Reponame"] = headRepo.Name
diff --git a/routers/web/repo/pull.go b/routers/web/repo/pull.go
index a299799647..703bbd837a 100644
--- a/routers/web/repo/pull.go
+++ b/routers/web/repo/pull.go
@@ -1001,10 +1001,14 @@ func CompareAndPullRequestPost(ctx *context.Context) {
 	ctx.Data["Title"] = ctx.Tr("repo.pulls.compare_changes")
 	ctx.Data["PageIsComparePull"] = true
 	ctx.Data["IsDiffCompare"] = true
+	ctx.Data["IsRepoToolbarCommits"] = true
+	ctx.Data["RequireTribute"] = true
+	ctx.Data["RequireSimpleMDE"] = true
 	ctx.Data["RequireHighlightJS"] = true
 	ctx.Data["PullRequestWorkInProgressPrefixes"] = setting.Repository.PullRequest.WorkInProgressPrefixes
 	ctx.Data["IsAttachmentEnabled"] = setting.Attachment.Enabled
 	upload.AddUploadContext(ctx, "comment")
+	ctx.Data["HasIssuesOrPullsWritePermission"] = ctx.Repo.CanWrite(models.UnitTypePullRequests)
 
 	var (
 		repo        = ctx.Repo.Repository
@@ -1037,6 +1041,14 @@ func CompareAndPullRequestPost(ctx *context.Context) {
 			return
 		}
 
+		if len(form.Title) > 255 {
+			var trailer string
+			form.Title, trailer = util.SplitStringAtByteN(form.Title, 255)
+
+			form.Content = trailer + "\n\n" + form.Content
+		}
+		middleware.AssignForm(form, ctx.Data)
+
 		ctx.HTML(http.StatusOK, tplCompareDiff)
 		return
 	}
diff --git a/templates/repo/diff/compare.tmpl b/templates/repo/diff/compare.tmpl
index 7959ef7bb5..2beca57960 100644
--- a/templates/repo/diff/compare.tmpl
+++ b/templates/repo/diff/compare.tmpl
@@ -176,10 +176,10 @@
 	{{if .IsNothingToCompare}}
 		{{if and $.IsSigned $.AllowEmptyPr (not .Repository.IsArchived) }}
 			<div class="ui segment">{{.i18n.Tr "repo.pulls.nothing_to_compare_and_allow_empty_pr"}}</div>
-			<div class="ui info message show-form-container">
+			<div class="ui info message show-form-container" {{if .Flash}}style="display: none"{{end}}>
 				<button class="ui button green show-form">{{.i18n.Tr "repo.pulls.new"}}</button>
 			</div>
-			<div class="pullrequest-form" style="display: none">
+			<div class="pullrequest-form" {{if not .Flash}}style="display: none"{{end}}>
 				{{template "repo/issue/new_form" .}}
 			</div>
 		{{else}}
@@ -192,7 +192,7 @@
 			</div>
 		{{else}}
 			{{if and $.IsSigned (not .Repository.IsArchived)}}
-				<div class="ui info message show-form-container">
+				<div class="ui info message show-form-container" {{if .Flash}}style="display: none"{{end}}>
 					<button class="ui button green show-form">{{.i18n.Tr "repo.pulls.new"}}</button>
 				</div>
 			{{else if .Repository.IsArchived}}
@@ -201,7 +201,7 @@
 				</div>
 			{{end}}
 			{{if $.IsSigned}}
-				<div class="pullrequest-form" style="display: none">
+				<div class="pullrequest-form" {{if not .Flash}}style="display: none"{{end}}>
 					{{template "repo/issue/new_form" .}}
 				</div>
 			{{end}}