diff --git a/hugolib/page_test.go b/hugolib/page_test.go
index 803dddc01..e32ef7399 100644
--- a/hugolib/page_test.go
+++ b/hugolib/page_test.go
@@ -2073,3 +2073,97 @@ foo
 	b, err := TestE(t, files)
 	b.Assert(err, qt.ErrorMatches, `.*template "view_bar" not found.*`)
 }
+
+// See issue 15057.
+func TestRenderCaseInsensitiveTemplateName(t *testing.T) {
+	t.Parallel()
+
+	files := `
+disableKinds = ['home','rss','section','sitemap','taxonomy','term']
+-- content/s1/p1.md --
+---
+title: p1
+---
+-- content/s2/p2.md --
+---
+title: p2
+layout: ab
+---
+-- content/s2/p3.md --
+---
+title: p3
+layout: aB
+---
+-- content/s2/p4.md --
+---
+title: p4
+layout: AB
+---
+-- content/s3/p5.md --
+---
+title: p5
+layout: cd
+---
+-- content/s3/p6.md --
+---
+title: p6
+layout: cD
+---
+-- content/s3/p7.md --
+---
+title: p7
+layout: CD
+---
+-- content/s4/p8.md --
+---
+title: p8
+layout: ef
+---
+-- content/s4/p9.md --
+---
+title: p9
+layout: eF
+---
+-- content/s4/p10.md --
+---
+title: p10
+layout: EF
+---
+-- layouts/s1/p1/page.html --
+{{ .Render "ab" }}|{{ .Render "aB" }}|{{ .Render "AB" }}
+{{ .Render "cd" }}|{{ .Render "cD" }}|{{ .Render "CD" }}
+{{ .Render "ef" }}|{{ .Render "eF" }}|{{ .Render "EF" }}
+-- layouts/s1/p1/ab.html --
+ab{{- /**/ -}}
+-- layouts/s1/p1/cD.html --
+cD{{- /**/ -}}
+-- layouts/s1/p1/EF.html --
+EF{{- /**/ -}}
+-- layouts/s2/ab.html --
+ab
+-- layouts/s3/cD.html --
+cD
+-- layouts/s4/EF.html --
+EF
+`
+
+	b := Test(t, files)
+
+	b.AssertFileContent("public/s1/p1/index.html",
+		"ab|ab|ab",
+		"cD|cD|cD",
+		"EF|EF|EF",
+	)
+
+	b.AssertFileContent("public/s2/p2/index.html", "ab")
+	b.AssertFileContent("public/s2/p3/index.html", "ab")
+	b.AssertFileContent("public/s2/p4/index.html", "ab")
+
+	b.AssertFileContent("public/s3/p5/index.html", "cD")
+	b.AssertFileContent("public/s3/p6/index.html", "cD")
+	b.AssertFileContent("public/s3/p7/index.html", "cD")
+
+	b.AssertFileContent("public/s4/p8/index.html", "EF")
+	b.AssertFileContent("public/s4/p9/index.html", "EF")
+	b.AssertFileContent("public/s4/p10/index.html", "EF")
+}
diff --git a/tpl/tplimpl/templatedescriptor.go b/tpl/tplimpl/templatedescriptor.go
index 1cfb8a31e..6a71ad3a6 100644
--- a/tpl/tplimpl/templatedescriptor.go
+++ b/tpl/tplimpl/templatedescriptor.go
@@ -14,6 +14,8 @@
 package tplimpl
 
 import (
+	"strings"
+
 	"github.com/gohugoio/hugo/common/types"
 	"github.com/gohugoio/hugo/hugolib/sitesmatrix"
 	"github.com/gohugoio/hugo/resources/kinds"
@@ -44,6 +46,8 @@ type TemplateDescriptor struct {
 }
 
 func (d *TemplateDescriptor) normalizeFromFile() {
+	d.LayoutFromTemplate = strings.ToLower(d.LayoutFromTemplate)
+
 	if d.LayoutFromTemplate == d.OutputFormat {
 		d.LayoutFromTemplate = ""
 	}
@@ -138,7 +142,7 @@ func (this TemplateDescriptor) doCompare(category Category, other TemplateDescri
 		// when one exist for the html output format (same media type).
 		skip := category != CategoryBaseof && (this.Kind == "" || (this.Kind != other.Kind && (this.LayoutFromTemplate != other.LayoutFromTemplate && other.LayoutFromTemplate != layoutAll)))
 		if this.LayoutFromUser != "" {
-			skip = skip && (this.LayoutFromUser != other.LayoutFromTemplate)
+			skip = skip && this.LayoutFromUser != other.LayoutFromTemplate
 		}
 		if skip {
 			return w
diff --git a/tpl/tplimpl/templatestore.go b/tpl/tplimpl/templatestore.go
index 0c324fd84..3b3fccff5 100644
--- a/tpl/tplimpl/templatestore.go
+++ b/tpl/tplimpl/templatestore.go
@@ -425,6 +425,7 @@ func (q *TemplateQuery) init() {
 	}
 
 	q.Name = strings.ToLower(q.Name)
+	q.Desc.LayoutFromUser = strings.ToLower(q.Desc.LayoutFromUser)
 
 	if q.Category == 0 {
 		panic("category not set")