diff --git a/hugolib/hugo_sites_build.go b/hugolib/hugo_sites_build.go
index cc8847f5591..1399e22d2a4 100644
--- a/hugolib/hugo_sites_build.go
+++ b/hugolib/hugo_sites_build.go
@@ -730,7 +730,7 @@ func (h *HugoSites) processPartial(ctx context.Context, l logg.LevelLogger, conf
 
 		case files.ComponentFolderLayouts:
 			tmplChanged = true
-			templatePath := pathInfo.TrimLeadingSlash().PathNoLang()
+			templatePath := pathInfo.Unnormalized().TrimLeadingSlash().PathNoLang()
 			if !h.Tmpl().HasTemplate(templatePath) {
 				tmplAdded = true
 			}
diff --git a/hugolib/rebuild_test.go b/hugolib/rebuild_test.go
index f3b10cf18cc..f2717644da9 100644
--- a/hugolib/rebuild_test.go
+++ b/hugolib/rebuild_test.go
@@ -1490,3 +1490,27 @@ title: "Default"
 	// Just make sure that it doesn't panic.
 	b.EditFileReplaceAll("archetypes/default.md", "Default", "Default Edited").Build()
 }
+
+func TestRebuildEditMixedCaseTemplateFileIssue12165(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+baseURL = "https://example.com"
+disableLiveReload = true
+-- layouts/partials/MyTemplate.html --
+MyTemplate
+-- layouts/index.html --
+MyTemplate: {{ partial "MyTemplate.html" . }}|
+
+
+`
+
+	b := TestRunning(t, files)
+
+	b.AssertFileContent("public/index.html", "MyTemplate: MyTemplate")
+
+	b.EditFileReplaceAll("layouts/partials/MyTemplate.html", "MyTemplate", "MyTemplate Edited").Build()
+
+	b.AssertFileContent("public/index.html", "MyTemplate: MyTemplate Edited")
+}