diff --git a/func.go b/func.go
index 02942a4..65cd7d9 100644
--- a/func.go
+++ b/func.go
@@ -240,7 +240,7 @@ func startwithFunc(arg1, arg2 query) func(query, iterator) interface{} {
 			m, n string
 			ok   bool
 		)
-		switch typ := arg1.Evaluate(t).(type) {
+		switch typ := functionArgs(arg1).Evaluate(t).(type) {
 		case string:
 			m = typ
 		case query:
@@ -252,7 +252,7 @@ func startwithFunc(arg1, arg2 query) func(query, iterator) interface{} {
 		default:
 			panic(errors.New("starts-with() function argument type must be string"))
 		}
-		n, ok = arg2.Evaluate(t).(string)
+		n, ok = functionArgs(arg2).Evaluate(t).(string)
 		if !ok {
 			panic(errors.New("starts-with() function argument type must be string"))
 		}
@@ -267,7 +267,7 @@ func endwithFunc(arg1, arg2 query) func(query, iterator) interface{} {
 			m, n string
 			ok   bool
 		)
-		switch typ := arg1.Evaluate(t).(type) {
+		switch typ := functionArgs(arg1).Evaluate(t).(type) {
 		case string:
 			m = typ
 		case query:
@@ -279,7 +279,7 @@ func endwithFunc(arg1, arg2 query) func(query, iterator) interface{} {
 		default:
 			panic(errors.New("ends-with() function argument type must be string"))
 		}
-		n, ok = arg2.Evaluate(t).(string)
+		n, ok = functionArgs(arg2).Evaluate(t).(string)
 		if !ok {
 			panic(errors.New("ends-with() function argument type must be string"))
 		}
@@ -294,8 +294,7 @@ func containsFunc(arg1, arg2 query) func(query, iterator) interface{} {
 			m, n string
 			ok   bool
 		)
-
-		switch typ := arg1.Evaluate(t).(type) {
+		switch typ := functionArgs(arg1).Evaluate(t).(type) {
 		case string:
 			m = typ
 		case query:
@@ -308,7 +307,7 @@ func containsFunc(arg1, arg2 query) func(query, iterator) interface{} {
 			panic(errors.New("contains() function argument type must be string"))
 		}
 
-		n, ok = arg2.Evaluate(t).(string)
+		n, ok = functionArgs(arg2).Evaluate(t).(string)
 		if !ok {
 			panic(errors.New("contains() function argument type must be string"))
 		}
@@ -345,7 +344,7 @@ func normalizespaceFunc(q query, t iterator) interface{} {
 func substringFunc(arg1, arg2, arg3 query) func(query, iterator) interface{} {
 	return func(q query, t iterator) interface{} {
 		var m string
-		switch typ := arg1.Evaluate(t).(type) {
+		switch typ := functionArgs(arg1).Evaluate(t).(type) {
 		case string:
 			m = typ
 		case query:
@@ -359,14 +358,14 @@ func substringFunc(arg1, arg2, arg3 query) func(query, iterator) interface{} {
 		var start, length float64
 		var ok bool
 
-		if start, ok = arg2.Evaluate(t).(float64); !ok {
+		if start, ok = functionArgs(arg2).Evaluate(t).(float64); !ok {
 			panic(errors.New("substring() function first argument type must be int"))
 		} else if start < 1 {
 			panic(errors.New("substring() function first argument type must be >= 1"))
 		}
 		start--
 		if arg3 != nil {
-			if length, ok = arg3.Evaluate(t).(float64); !ok {
+			if length, ok = functionArgs(arg3).Evaluate(t).(float64); !ok {
 				panic(errors.New("substring() function second argument type must be int"))
 			}
 		}
@@ -384,7 +383,7 @@ func substringFunc(arg1, arg2, arg3 query) func(query, iterator) interface{} {
 func substringIndFunc(arg1, arg2 query, after bool) func(query, iterator) interface{} {
 	return func(q query, t iterator) interface{} {
 		var str string
-		switch v := arg1.Evaluate(t).(type) {
+		switch v := functionArgs(arg1).Evaluate(t).(type) {
 		case string:
 			str = v
 		case query:
@@ -395,7 +394,7 @@ func substringIndFunc(arg1, arg2 query, after bool) func(query, iterator) interf
 			str = node.Value()
 		}
 		var word string
-		switch v := arg2.Evaluate(t).(type) {
+		switch v := functionArgs(arg2).Evaluate(t).(type) {
 		case string:
 			word = v
 		case query:
@@ -424,7 +423,7 @@ func substringIndFunc(arg1, arg2 query, after bool) func(query, iterator) interf
 // equal to the number of characters in a given string.
 func stringLengthFunc(arg1 query) func(query, iterator) interface{} {
 	return func(q query, t iterator) interface{} {
-		switch v := arg1.Evaluate(t).(type) {
+		switch v := functionArgs(arg1).Evaluate(t).(type) {
 		case string:
 			return float64(len(v))
 		case query:
@@ -441,9 +440,9 @@ func stringLengthFunc(arg1 query) func(query, iterator) interface{} {
 // translateFunc is XPath functions translate() function returns a replaced string.
 func translateFunc(arg1, arg2, arg3 query) func(query, iterator) interface{} {
 	return func(q query, t iterator) interface{} {
-		str := asString(t, arg1.Evaluate(t))
-		src := asString(t, arg2.Evaluate(t))
-		dst := asString(t, arg3.Evaluate(t))
+		str := asString(t, functionArgs(arg1).Evaluate(t))
+		src := asString(t, functionArgs(arg2).Evaluate(t))
+		dst := asString(t, functionArgs(arg3).Evaluate(t))
 
 		var replace []string
 		for i, s := range src {
@@ -460,9 +459,9 @@ func translateFunc(arg1, arg2, arg3 query) func(query, iterator) interface{} {
 // replaceFunc is XPath functions replace() function returns a replaced string.
 func replaceFunc(arg1, arg2, arg3 query) func(query, iterator) interface{} {
 	return func(q query, t iterator) interface{} {
-		str := asString(t, arg1.Evaluate(t))
-		src := asString(t, arg2.Evaluate(t))
-		dst := asString(t, arg3.Evaluate(t))
+		str := asString(t, functionArgs(arg1).Evaluate(t))
+		src := asString(t, functionArgs(arg2).Evaluate(t))
+		dst := asString(t, functionArgs(arg3).Evaluate(t))
 
 		return strings.Replace(str, src, dst, -1)
 	}
@@ -488,6 +487,7 @@ func concatFunc(args ...query) func(query, iterator) interface{} {
 	return func(q query, t iterator) interface{} {
 		var a []string
 		for _, v := range args {
+			v = functionArgs(v)
 			switch v := v.Evaluate(t).(type) {
 			case string:
 				a = append(a, v)
@@ -501,3 +501,11 @@ func concatFunc(args ...query) func(query, iterator) interface{} {
 		return strings.Join(a, "")
 	}
 }
+
+// https://github.com/antchfx/xpath/issues/43
+func functionArgs(q query) query {
+	if _, ok := q.(*functionQuery); ok {
+		return q
+	}
+	return q.Clone()
+}