diff --git a/pkg/expr/mongo.go b/pkg/expr/mongo.go
index 3cdbf0452c285402f64600b008bafd572045bd99..de14bb57a6e7609b6f770d8318abbdc1ca02694b 100644
--- a/pkg/expr/mongo.go
+++ b/pkg/expr/mongo.go
@@ -231,19 +231,12 @@ func (c *compiler) identifier(node ast.Node) string {
 }
 
 func (c *compiler) BinaryNode(node *ast.BinaryNode) interface{} {
+	if result, ok := c.handleLenNode(node); ok {
+		return result
+	}
+
 	switch node.Operator {
 	case "==":
-		op := c.eval(node.Right)
-		lenNode, ok := node.Left.(*ast.BuiltinNode)
-		if ok && lenNode.Name == "len" && len(lenNode.Arguments) == 1 {
-			// Оптимизация для случая len(arr) == 0, т.к. $size не использует индекс
-			if op == 0 {
-				return bson.M{c.identifier(lenNode.Arguments[0]): bson.M{"$eq": bson.A{}}}
-			}
-
-			return bson.M{c.identifier(lenNode.Arguments[0]): bson.M{"$size": op}}
-		}
-
 		return bson.M{c.identifier(node.Left): c.eval(node.Right)}
 
 	case "!=":
@@ -262,36 +255,10 @@ func (c *compiler) BinaryNode(node *ast.BinaryNode) interface{} {
 		return bson.M{c.identifier(node.Left): bson.M{"$nin": c.eval(node.Right)}}
 
 	case "<":
-		op := c.eval(node.Right)
-		lenNode, ok := node.Left.(*ast.BuiltinNode)
-		if ok && lenNode.Name == "len" && len(lenNode.Arguments) == 1 {
-			length, ok := op.(int)
-			if !ok {
-				panic("len must be compared with an integer")
-			}
-			return bson.M{c.identifier(lenNode.Arguments[0]) + "." + strconv.Itoa(length): bson.M{"$exists": false}}
-		}
-
 		return bson.M{c.identifier(node.Left): bson.M{"$lt": c.eval(node.Right)}}
 
 	case ">":
-		op := c.eval(node.Right)
-		lenNode, ok := node.Left.(*ast.BuiltinNode)
-		if ok && lenNode.Name == "len" && len(lenNode.Arguments) == 1 {
-			length, ok := op.(int)
-			if !ok {
-				panic("len must be compared with an integer")
-			}
-
-			// Оптимизация для случая len(arr) > 0
-			if length == 0 {
-				return bson.M{c.identifier(lenNode.Arguments[0]): bson.M{"$exists": true, "$type": "array", "$ne": bson.A{}}}
-			}
-
-			return bson.M{c.identifier(lenNode.Arguments[0]) + "." + strconv.Itoa(length): bson.M{"$exists": true}}
-		}
-
-		return bson.M{c.identifier(node.Left): bson.M{"$gt": op}}
+		return bson.M{c.identifier(node.Left): bson.M{"$gt": c.eval(node.Right)}}
 
 	case "<=":
 		return bson.M{c.identifier(node.Left): bson.M{"$lte": c.eval(node.Right)}}
@@ -688,3 +655,56 @@ func (c *compiler) PairNode(node *ast.PairNode) interface{} {
 	//c.compile(node.Key)
 	//c.compile(node.Value)
 }
+
+func (c *compiler) handleLenNode(node *ast.BinaryNode) (result bson.M, ok bool) {
+	lenNode, ok := node.Left.(*ast.BuiltinNode)
+	if !ok || lenNode.Name != "len" {
+		return nil, false
+	}
+
+	if len(lenNode.Arguments) != 1 {
+		panic("len() expects exactly 1 argument")
+	}
+
+	length, ok := c.eval(node.Right).(int)
+	if !ok || length < 0 {
+		panic("len() can only be compared with non-negative number")
+	}
+
+	switch node.Operator {
+	case "==": // +
+		if length == 0 {
+			return bson.M{c.identifier(lenNode.Arguments[0]): bson.M{"$eq": bson.A{}}}, true
+		}
+		return bson.M{c.identifier(lenNode.Arguments[0]): bson.M{"$size": length}}, true
+
+	case "!=": // +
+		if length == 0 {
+			return bson.M{c.identifier(lenNode.Arguments[0]): bson.M{"$exists": true, "$type": "array", "$ne": bson.A{}}}, true
+		}
+		return bson.M{c.identifier(lenNode.Arguments[0]): bson.M{"$not": bson.M{"$size": length}}}, true
+
+	case ">": // +
+		if length == 0 {
+			return bson.M{c.identifier(lenNode.Arguments[0]): bson.M{"$exists": true, "$type": "array", "$ne": bson.A{}}}, true
+		}
+		return bson.M{c.identifier(lenNode.Arguments[0]) + "." + strconv.Itoa(length): bson.M{"$exists": true}}, true
+
+	case ">=":
+		if length == 0 {
+			return bson.M{c.identifier(lenNode.Arguments[0]): bson.M{"$exists": true, "$type": "array"}}, true
+		}
+		return bson.M{c.identifier(lenNode.Arguments[0]) + "." + strconv.Itoa(length-1): bson.M{"$exists": true}}, true
+
+	case "<":
+		if length == 0 {
+			panic("invalid comparison: len() cannot be less than 0")
+		}
+		return bson.M{c.identifier(lenNode.Arguments[0]) + "." + strconv.Itoa(length-1): bson.M{"$exists": false}}, true
+
+	case "<=":
+		return bson.M{c.identifier(lenNode.Arguments[0]) + "." + strconv.Itoa(length): bson.M{"$exists": false}}, true
+	}
+
+	panic("invalid comparison operator with len()")
+}
diff --git a/pkg/expr/mongo_test.go b/pkg/expr/mongo_test.go
index c8f8d4baf7a7a6b672452310705dfb3e20d61e06..ae6bee1681fe3bed38d2743d80cfe6a835961701 100644
--- a/pkg/expr/mongo_test.go
+++ b/pkg/expr/mongo_test.go
@@ -35,7 +35,7 @@ func TestConvertToMongo(t *testing.T) {
 		{"len equal empty", "len(s) == 0", nil, bson.M{"s": bson.M{"$eq": bson.A{}}}, false},
 		{"len gt", "len(s) > 1", nil, bson.M{"s.1": bson.M{"$exists": true}}, false},
 		{"len gt 0", "len(s) > 0", nil, bson.M{"s": bson.M{"$exists": true, "$type": "array", "$ne": bson.A{}}}, false},
-		{"len lt", "len(s) < 1", nil, bson.M{"s.1": bson.M{"$exists": false}}, false},
+		{"len lt", "len(s) < 1", nil, bson.M{"s.0": bson.M{"$exists": false}}, false},
 		{"field#1", "s.test > 3", nil, bson.M{"s.test": bson.M{"$gt": 3}}, false},
 		{"field#2", "s['test'] > 3", nil, bson.M{"s.test": bson.M{"$gt": 3}}, false},
 		{"field#3", "s[test] > 3", nil, bson.M{"s.test": bson.M{"$gt": 3}}, false},