diff --git a/modules/markup/html.go b/modules/markup/html.go
index 216a1f20a..7b9844bf7 100644
--- a/modules/markup/html.go
+++ b/modules/markup/html.go
@@ -401,7 +401,7 @@ func (ctx *postProcessCtx) visitNode(node *html.Node, visitText bool) {
 		}
 	case html.ElementNode:
 		if node.Data == "img" {
-			for _, attr := range node.Attr {
+			for i, attr := range node.Attr {
 				if attr.Key != "src" {
 					continue
 				}
@@ -414,6 +414,7 @@ func (ctx *postProcessCtx) visitNode(node *html.Node, visitText bool) {
 
 					attr.Val = util.URLJoin(prefix, attr.Val)
 				}
+				node.Attr[i] = attr
 			}
 		} else if node.Data == "a" {
 			visitText = false
diff --git a/modules/markup/html_test.go b/modules/markup/html_test.go
index 4d6344a72..dddb3ade0 100644
--- a/modules/markup/html_test.go
+++ b/modules/markup/html_test.go
@@ -384,6 +384,32 @@ func TestRender_ShortLinks(t *testing.T) {
 		`<p><a href="https://example.org" rel="nofollow">[[foobar]]</a></p>`)
 }
 
+func TestRender_RelativeImages(t *testing.T) {
+	setting.AppURL = AppURL
+	setting.AppSubURL = AppSubURL
+	tree := util.URLJoin(AppSubURL, "src", "master")
+
+	test := func(input, expected, expectedWiki string) {
+		buffer := markdown.RenderString(input, tree, localMetas)
+		assert.Equal(t, strings.TrimSpace(expected), strings.TrimSpace(buffer))
+		buffer = markdown.RenderWiki([]byte(input), setting.AppSubURL, localMetas)
+		assert.Equal(t, strings.TrimSpace(expectedWiki), strings.TrimSpace(buffer))
+	}
+
+	rawwiki := util.URLJoin(AppSubURL, "wiki", "raw")
+	mediatree := util.URLJoin(AppSubURL, "media", "master")
+
+	test(
+		`<img src="Link">`,
+		`<img src="`+util.URLJoin(mediatree, "Link")+`"/>`,
+		`<img src="`+util.URLJoin(rawwiki, "Link")+`"/>`)
+
+	test(
+		`<img src="./icon.png">`,
+		`<img src="`+util.URLJoin(mediatree, "icon.png")+`"/>`,
+		`<img src="`+util.URLJoin(rawwiki, "icon.png")+`"/>`)
+}
+
 func Test_ParseClusterFuzz(t *testing.T) {
 	setting.AppURL = AppURL
 	setting.AppSubURL = AppSubURL