diff --git a/markup/highlight/config.go b/markup/highlight/config.go
index 9013dd072..b1f6d4603 100644
--- a/markup/highlight/config.go
+++ b/markup/highlight/config.go
@@ -198,7 +198,7 @@ func parseHightlightOptions(in string) (map[string]any, error) {
 
 	for _, v := range strings.Split(in, ",") {
 		keyVal := strings.Split(v, "=")
-		key := strings.ToLower(strings.Trim(keyVal[0], " "))
+		key := strings.Trim(keyVal[0], " ")
 		if len(keyVal) != 2 {
 			return opts, fmt.Errorf("invalid Highlight option: %s", key)
 		}
@@ -216,6 +216,12 @@ func normalizeHighlightOptions(m map[string]any) {
 		return
 	}
 
+	// lowercase all keys
+	for k, v := range m {
+		delete(m, k)
+		m[strings.ToLower(k)] = v
+	}
+
 	baseLineNumber := 1
 	if v, ok := m[linosStartKey]; ok {
 		baseLineNumber = cast.ToInt(v)
@@ -232,7 +238,6 @@ func normalizeHighlightOptions(m map[string]any) {
 			if vs, ok := v.(string); ok {
 				m[k] = vs != "false"
 			}
-
 		case hlLinesKey:
 			if hlRanges, ok := v.([][2]int); ok {
 				for i := range hlRanges {
diff --git a/markup/highlight/config_test.go b/markup/highlight/config_test.go
index ab92ecf36..23da29ab6 100644
--- a/markup/highlight/config_test.go
+++ b/markup/highlight/config_test.go
@@ -53,4 +53,21 @@ func TestConfig(t *testing.T) {
 		c.Assert(cfg.LineNoStart, qt.Equals, 32)
 		c.Assert(cfg.Hl_Lines, qt.Equals, "3-8 10-20")
 	})
+
+	c.Run("applyOptionsFromMap", func(c *qt.C) {
+		cfg := DefaultConfig
+		err := applyOptionsFromMap(map[string]any{
+			"noclasses":   true,
+			"lineNos":     "inline", // mixed case key, should work after normalization
+			"linenostart": 32,
+			"hl_lines":    "3-8 10-20",
+		}, &cfg)
+
+		c.Assert(err, qt.IsNil)
+		c.Assert(cfg.NoClasses, qt.Equals, true)
+		c.Assert(cfg.LineNos, qt.Equals, true)
+		c.Assert(cfg.LineNumbersInTable, qt.Equals, false)
+		c.Assert(cfg.LineNoStart, qt.Equals, 32)
+		c.Assert(cfg.Hl_Lines, qt.Equals, "3-8 10-20")
+	})
 }