diff --git a/pkg/compiler/compiler_func_test.go b/pkg/compiler/compiler_func_test.go
index cc402ff0..bf185bdd 100644
--- a/pkg/compiler/compiler_func_test.go
+++ b/pkg/compiler/compiler_func_test.go
@@ -6,54 +6,43 @@ import (
 
 func TestFunctionCall(t *testing.T) {
 	RunUseCases(t, []UseCase{
+		//{
+		//	"RETURN TYPENAME(1)",
+		//	"int",
+		//	nil,
+		//},
+		//{
+		//	"WAIT(10) RETURN 1",
+		//	1,
+		//	nil,
+		//},
+		//{
+		//	"LET duration = 10 WAIT(duration) RETURN 1",
+		//	1,
+		//	nil,
+		//},
 		{
-			"RETURN TYPENAME(1)",
-			"int",
+			"RETURN (FALSE OR T::FAIL())?",
 			nil,
-		},
-		{
-			"WAIT(10) RETURN 1",
-			1,
 			nil,
 		},
 		{
-			"LET duration = 10 WAIT(duration) RETURN 1",
-			1,
+			"RETURN T::FAIL()?",
+			nil,
 			nil,
 		},
 		//{
-		//	"RETURN (FALSE OR T::FAIL())?",
-		//	nil,
-		//	nil,
-		//},
-		//{
-		//	"RETURN ERROR()?",
-		//	nil,
-		//	nil,
+		//	`FOR i IN [1, 2, 3, 4]
+		//		LET duration = 10
+		//
+		//		WAIT(duration)
+		//
+		//		RETURN i * 2`,
+		//	[]int{2, 4, 6, 8},
+		//	ShouldEqualJSON,
 		//},
 	})
 
-	//
-	//Convey("Should compile function call inside FOR IN statement", t, func() {
-	//	c := compiler.New()
-	//
-	//	p, err := c.Compile(`
-	//		FOR i IN [1, 2, 3, 4]
-	//			LET duration = 10
-	//
-	//			WAIT(duration)
-	//
-	//			RETURN i * 2
-	//	`)
-	//
-	//	So(err, ShouldBeNil)
-	//
-	//	out, err := p.Run(context.Background())
-	//
-	//	So(err, ShouldBeNil)
-	//
-	//	So(string(out), ShouldEqual, `[2,4,6,8]`)
-	//})
 	//
 	//Convey("Should handle errors when ? is used", t, func() {
 	//	c := compiler.New()
diff --git a/pkg/compiler/visitor.go b/pkg/compiler/visitor.go
index 902fb95f..2c51d11f 100644
--- a/pkg/compiler/visitor.go
+++ b/pkg/compiler/visitor.go
@@ -297,7 +297,7 @@ func (v *visitor) VisitFunctionCallExpression(ctx *fql.FunctionCallExpressionCon
 
 	name += call.FunctionName().GetText()
 
-	//regularCall := ctx.ErrorOperator() == nil
+	isNonOptional := ctx.ErrorOperator() == nil
 
 	v.emit(runtime.OpConstant, v.addConstant(values.String(name)))
 
@@ -310,17 +310,41 @@ func (v *visitor) VisitFunctionCallExpression(ctx *fql.FunctionCallExpressionCon
 
 	switch size {
 	case 0:
-		v.emit(runtime.OpCall, 0)
+		if isNonOptional {
+			v.emit(runtime.OpCall, 0)
+		} else {
+			v.emit(runtime.OpCallOptional, 0)
+		}
 	case 1:
-		v.emit(runtime.OpCall1, 1)
+		if isNonOptional {
+			v.emit(runtime.OpCall1, 1)
+		} else {
+			v.emit(runtime.OpCall1Optional, 1)
+		}
 	case 2:
-		v.emit(runtime.OpCall2, 2)
+		if isNonOptional {
+			v.emit(runtime.OpCall2, 2)
+		} else {
+			v.emit(runtime.OpCall2Optional, 2)
+		}
 	case 3:
-		v.emit(runtime.OpCall3, 3)
+		if isNonOptional {
+			v.emit(runtime.OpCall3, 3)
+		} else {
+			v.emit(runtime.OpCall3Optional, 3)
+		}
 	case 4:
-		v.emit(runtime.OpCall4, 4)
+		if isNonOptional {
+			v.emit(runtime.OpCall4, 4)
+		} else {
+			v.emit(runtime.OpCall4Optional, 4)
+		}
 	default:
-		v.emit(runtime.OpCallN, size)
+		if isNonOptional {
+			v.emit(runtime.OpCallN, size)
+		} else {
+			v.emit(runtime.OpCallNOptional, size)
+		}
 	}
 
 	return nil
diff --git a/pkg/runtime/opcodes.go b/pkg/runtime/opcodes.go
index f89c9420..e95883c7 100644
--- a/pkg/runtime/opcodes.go
+++ b/pkg/runtime/opcodes.go
@@ -42,11 +42,17 @@ const (
 	OpRegexpPositive
 	OpRegexpNegative
 	OpCall
+	OpCallOptional
 	OpCall1
+	OpCall1Optional
 	OpCall2
+	OpCall2Optional
 	OpCall3
+	OpCall3Optional
 	OpCall4
+	OpCall4Optional
 	OpCallN
+	OpCallNOptional
 	OpPush
 	OpPop
 	OpPopClose
diff --git a/pkg/runtime/vm.go b/pkg/runtime/vm.go
index 5556321f..166edd7d 100644
--- a/pkg/runtime/vm.go
+++ b/pkg/runtime/vm.go
@@ -283,28 +283,32 @@ loop:
 			reg := program.Constants[arg].(*values.Regexp)
 			stack.Push(!reg.Match(stack.Pop()))
 
-		case OpCall:
+		case OpCall, OpCallOptional:
 			fnName := stack.Pop().String()
 			res, err := vm.env.GetFunction(fnName)(ctx)
 
 			if err == nil {
 				stack.Push(res)
+			} else if op == OpCallOptional {
+				stack.Push(values.None)
 			} else {
 				return nil, err
 			}
 
-		case OpCall1:
+		case OpCall1, OpCall1Optional:
 			arg := stack.Pop()
 			fnName := stack.Pop().String()
 			res, err := vm.env.GetFunction(fnName)(ctx, arg)
 
 			if err == nil {
 				stack.Push(res)
+			} else if op == OpCall1Optional {
+				stack.Push(values.None)
 			} else {
 				return nil, err
 			}
 
-		case OpCall2:
+		case OpCall2, OpCall2Optional:
 			arg2 := stack.Pop()
 			arg1 := stack.Pop()
 			fnName := stack.Pop().String()
@@ -312,11 +316,13 @@ loop:
 
 			if err == nil {
 				stack.Push(res)
+			} else if op == OpCall2Optional {
+				stack.Push(values.None)
 			} else {
 				return nil, err
 			}
 
-		case OpCall3:
+		case OpCall3, OpCall3Optional:
 			arg3 := stack.Pop()
 			arg2 := stack.Pop()
 			arg1 := stack.Pop()
@@ -325,11 +331,13 @@ loop:
 
 			if err == nil {
 				stack.Push(res)
+			} else if op == OpCall3Optional {
+				stack.Push(values.None)
 			} else {
 				return nil, err
 			}
 
-		case OpCall4:
+		case OpCall4, OpCall4Optional:
 			arg4 := stack.Pop()
 			arg3 := stack.Pop()
 			arg2 := stack.Pop()
@@ -339,10 +347,12 @@ loop:
 
 			if err == nil {
 				stack.Push(res)
+			} else if op == OpCall4Optional {
+				stack.Push(values.None)
 			} else {
 				return nil, err
 			}
-		case OpCallN:
+		case OpCallN, OpCallNOptional:
 			// pop arguments from the stack
 			// and push them to the arguments array
 			// in reverse order because stack is LIFO and arguments array is FIFO
@@ -361,6 +371,8 @@ loop:
 
 			if err == nil {
 				stack.Push(res)
+			} else if op == OpCallNOptional {
+				stack.Push(values.None)
 			} else {
 				return nil, err
 			}