diff --git a/hugolib/case_insensitive_test.go b/hugolib/case_insensitive_test.go
index f3ba5f933..8c94bf5db 100644
--- a/hugolib/case_insensitive_test.go
+++ b/hugolib/case_insensitive_test.go
@@ -125,6 +125,7 @@ Shortcode Site: {{ .Page.Site.Params.COLOR }}|{{ .Site.Params.COLORS.YELLOW  }}
 	writeToFs(t, fs, "layouts/partials/partial.html", `
 Partial Page: {{ .Params.COLOR }}|{{ .Params.Colors.Blue }}
 Partial Site: {{ .Site.Params.COLOR }}|{{ .Site.Params.COLORS.YELLOW }}
+Partial Site Global: {{ site.Params.COLOR }}|{{ site.Params.COLORS.YELLOW }}
 `)
 
 	writeToFs(t, fs, "config.toml", caseMixingSiteConfigTOML)
@@ -200,6 +201,7 @@ Site Colors: {{ .Site.Params.COLOR }}|{{ .Site.Params.COLORS.YELLOW }}
 		"Shortcode Site: green|yellow",
 		"Partial Page: red|heavenly",
 		"Partial Site: green|yellow",
+		"Partial Site Global: green|yellow",
 		"Page Title: Side 1",
 		"Site Title: Nynorsk title",
 		"«Hi»", // angled quotes
diff --git a/tpl/tplimpl/template_ast_transformers.go b/tpl/tplimpl/template_ast_transformers.go
index 1e1589308..f32b189ff 100644
--- a/tpl/tplimpl/template_ast_transformers.go
+++ b/tpl/tplimpl/template_ast_transformers.go
@@ -130,8 +130,12 @@ func (c *templateContext) paramsKeysToLower(n parse.Node) {
 				c.updateIdentsIfNeeded(an.Ident)
 			case *parse.PipeNode:
 				c.paramsKeysToLower(an)
+			case *parse.ChainNode:
+				// site.Params...
+				if len(an.Field) > 1 && an.Field[0] == paramsIdentifier {
+					c.updateIdentsIfNeeded(an.Field)
+				}
 			}
-
 		}
 	}
 }
diff --git a/tpl/tplimpl/template_ast_transformers_test.go b/tpl/tplimpl/template_ast_transformers_test.go
index 52d8c17b1..45cf4399a 100644
--- a/tpl/tplimpl/template_ast_transformers_test.go
+++ b/tpl/tplimpl/template_ast_transformers_test.go
@@ -34,6 +34,13 @@ var (
 				"ByWeight": fmt.Sprintf("%v:%v:%v", seq, key, args),
 			}, nil
 		},
+		"site": func() interface{} {
+			return map[string]interface{}{
+				"Params": map[string]interface{}{
+					"lower": "global-site",
+				},
+			}
+		},
 	}
 
 	paramsData = map[string]interface{}{
@@ -154,6 +161,12 @@ PARAMS TIME: {{ $time.Format "2006-01-02" }}
 
 {{ $_x :=  $.Params.MyDate | ToTime }}
 PARAMS TIME2: {{ $_x.AddDate 0 1 0 }}
+
+PARAMS SITE GLOBAL1: {{ site.Params.LOwER }}
+{{ $lower := site.Params.LOwER }}
+{{ $site := site }}
+PARAMS SITE GLOBAL2: {{ $lower }}
+PARAMS SITE GLOBAL3: {{ $site.Params.LOWER }}
 `
 )
 
@@ -225,6 +238,11 @@ func TestParamsKeysToLower(t *testing.T) {
 	require.Contains(t, result, "PARAMS TIME: 1972-02-28")
 	require.Contains(t, result, "PARAMS TIME2: 1972-02-28")
 
+	// Issue ##5615
+	require.Contains(t, result, "PARAMS SITE GLOBAL1: global-site")
+	require.Contains(t, result, "PARAMS SITE GLOBAL2: global-site")
+	require.Contains(t, result, "PARAMS SITE GLOBAL3: global-site")
+
 }
 
 func BenchmarkTemplateParamsKeysToLower(b *testing.B) {