diff --git a/hugolib/alias.go b/hugolib/alias.go
index 58d908ce6..32058833e 100644
--- a/hugolib/alias.go
+++ b/hugolib/alias.go
@@ -96,7 +96,7 @@ func (s *Site) writeDestAlias(path, permalink string, outputFormat output.Format
 func (s *Site) publishDestAlias(allowRoot bool, path, permalink string, outputFormat output.Format, p page.Page) (err error) {
 	handler := newAliasHandler(s.GetTemplateStore(), s.Log, allowRoot)
 
-	targetPath, err := handler.targetPathAlias(path)
+	targetPath, err := handler.targetPathAlias(path, outputFormat)
 	if err != nil {
 		return err
 	}
@@ -120,7 +120,7 @@ func (s *Site) publishDestAlias(allowRoot bool, path, permalink string, outputFo
 	return s.publisher.Publish(pd)
 }
 
-func (a aliasHandler) targetPathAlias(src string) (string, error) {
+func (a aliasHandler) targetPathAlias(src string, of output.Format) (string, error) {
 	originalAlias := src
 	if len(src) <= 0 {
 		return "", fmt.Errorf("alias \"\" is an empty string")
@@ -176,13 +176,23 @@ func (a aliasHandler) targetPathAlias(src string) (string, error) {
 		}
 	}
 
-	// Add the final touch
+	// Add the final touch. When the alias does not already end in one of the
+	// output format's configured suffixes, treat it as a directory and append
+	// the format's base name and suffix (e.g. index.html).
 	alias = strings.TrimPrefix(alias, "/")
+	baseFile := of.BaseName + of.MediaType.FirstSuffix.FullSuffix
 	if strings.HasSuffix(alias, "/") {
-		alias = alias + "index.html"
-	} else if !strings.HasSuffix(alias, ".html") {
-		alias = alias + "/" + "index.html"
+		alias = alias + baseFile
+	} else if !pathHasOutputFormatSuffix(alias, of) {
+		alias = alias + "/" + baseFile
 	}
 
 	return filepath.FromSlash(alias), nil
 }
+
+// pathHasOutputFormatSuffix reports whether the last element of p ends in one
+// of the suffixes configured for the output format's media type.
+func pathHasOutputFormatSuffix(p string, of output.Format) bool {
+	ext := path.Ext(p)
+	return ext != "" && of.MediaType.HasSuffix(ext[1:])
+}
diff --git a/hugolib/alias_test.go b/hugolib/alias_test.go
index 977c6d9e1..e9bfe8e6c 100644
--- a/hugolib/alias_test.go
+++ b/hugolib/alias_test.go
@@ -21,6 +21,7 @@ import (
 
 	"github.com/gohugoio/hugo/common/loggers"
 	"github.com/gohugoio/hugo/config"
+	"github.com/gohugoio/hugo/output"
 )
 
 func TestAlias(t *testing.T) {
@@ -158,7 +159,7 @@ func TestTargetPathHTMLRedirectAlias(t *testing.T) {
 	}
 
 	for _, test := range tests {
-		path, err := h.targetPathAlias(test.value)
+		path, err := h.targetPathAlias(test.value, output.HTMLFormat)
 		if (err == nil) != test.errIsNil {
 			t.Errorf("Expected err == nil => %t, got: %t. err: %s", test.errIsNil, err == nil, err)
 			continue
@@ -789,3 +790,78 @@ build:
 	b.AssertFileExists("public/p2-alias/index.html", false)
 	b.AssertFileExists("public/p3-alias/index.html", false)
 }
+
+// See issue 15066.
+func TestAliasExplicitExtension(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+disableKinds = ['home','rss','section','sitemap','taxonomy','term']
+uglyURLs = UGLYURLS
+
+[mediaTypes]
+  [mediaTypes.'text/html']
+    suffixes = SUFFIXES
+
+[outputFormats]
+  [outputFormats.html]
+    mediaType = 'text/html'
+
+-- content/s1/p1.md --
+---
+title: p1
+aliases: [a, b.foo, c.html, d.htm, e.foo.html, f.foo.htm]
+---
+-- layouts/page.html --
+{{ .Title }}
+`
+
+	r := strings.NewReplacer("UGLYURLS", "false", "SUFFIXES", "['html', 'htm']")
+	f := r.Replace(files)
+
+	b := Test(t, f)
+
+	b.AssertFileContent("public/s1/a/index.html", "url=/s1/p1/")
+	b.AssertFileContent("public/s1/b.foo/index.html", "url=/s1/p1/")
+	b.AssertFileContent("public/s1/c.html", "url=/s1/p1/")
+	b.AssertFileContent("public/s1/d.htm", "url=/s1/p1/")
+	b.AssertFileContent("public/s1/e.foo.html", "url=/s1/p1/")
+	b.AssertFileContent("public/s1/f.foo.htm", "url=/s1/p1/")
+
+	r = strings.NewReplacer("UGLYURLS", "false", "SUFFIXES", "['htm', 'html']")
+	f = r.Replace(files)
+
+	b = Test(t, f)
+
+	b.AssertFileContent("public/s1/a/index.htm", "url=/s1/p1/")
+	b.AssertFileContent("public/s1/b.foo/index.htm", "url=/s1/p1/")
+	b.AssertFileContent("public/s1/c.html", "url=/s1/p1/")
+	b.AssertFileContent("public/s1/d.htm", "url=/s1/p1/")
+	b.AssertFileContent("public/s1/e.foo.html", "url=/s1/p1/")
+	b.AssertFileContent("public/s1/f.foo.htm", "url=/s1/p1/")
+
+	r = strings.NewReplacer("UGLYURLS", "true", "SUFFIXES", "['html', 'htm']")
+	f = r.Replace(files)
+
+	b = Test(t, f)
+
+	b.AssertFileContent("public/s1/a.html", "url=/s1/p1.html")
+	b.AssertFileContent("public/s1/b.foo.html", "url=/s1/p1.html")
+	b.AssertFileContent("public/s1/c.html", "url=/s1/p1.html")
+	b.AssertFileContent("public/s1/d.htm", "url=/s1/p1.html")
+	b.AssertFileContent("public/s1/e.foo.html", "url=/s1/p1.html")
+	b.AssertFileContent("public/s1/f.foo.htm", "url=/s1/p1.html")
+
+	r = strings.NewReplacer("UGLYURLS", "true", "SUFFIXES", "['htm', 'html']")
+	f = r.Replace(files)
+
+	b = Test(t, f)
+
+	b.AssertFileContent("public/s1/a.htm", "url=/s1/p1.htm")
+	b.AssertFileContent("public/s1/b.foo.htm", "url=/s1/p1.htm")
+	b.AssertFileContent("public/s1/c.html", "url=/s1/p1.htm")
+	b.AssertFileContent("public/s1/d.htm", "url=/s1/p1.htm")
+	b.AssertFileContent("public/s1/e.foo.html", "url=/s1/p1.htm")
+	b.AssertFileContent("public/s1/f.foo.htm", "url=/s1/p1.htm")
+}
diff --git a/hugolib/page__output.go b/hugolib/page__output.go
index 979fb755b..384ed5f9e 100644
--- a/hugolib/page__output.go
+++ b/hugolib/page__output.go
@@ -140,8 +140,8 @@ func (po *pageOutput) Aliases() []string {
 
 		a = path.Join(baseDir, a)
 
-		if conf.C.IsUglyURLSection(p.Section()) && !strings.HasSuffix(a, ".html") {
-			a += ".html"
+		if conf.C.IsUglyURLSection(p.Section()) && !pathHasOutputFormatSuffix(a, f) {
+			a += f.MediaType.FirstSuffix.FullSuffix
 		}
 
 		aliases[i] = a