diff --git a/builtin/builtin.go b/builtin/builtin.go
index 2417446d..cd943bd0 100644
--- a/builtin/builtin.go
+++ b/builtin/builtin.go
@@ -13,12 +13,13 @@ import (
 )
 
 type Function struct {
-	Name      string
-	Func      func(args ...any) (any, error)
-	Fast      func(arg any) any
-	Types     []reflect.Type
-	Validate  func(args []reflect.Type) (reflect.Type, error)
-	Predicate bool
+	Name         string
+	Func         func(args ...any) (any, error)
+	Fast         func(arg any) any
+	ValidateArgs func(args ...any) (any, error)
+	Types        []reflect.Type
+	Validate     func(args []reflect.Type) (reflect.Type, error)
+	Predicate    bool
 }
 
 var (
@@ -325,12 +326,15 @@ var Builtins = []*Function{
 	},
 	{
 		Name: "repeat",
-		Func: func(args ...any) (any, error) {
+		ValidateArgs: func(args ...any) (any, error) {
 			n := runtime.ToInt(args[1])
-			if n > 1e6 {
-				panic("memory budget exceeded")
+			if n < 0 {
+				panic(fmt.Errorf("invalid argument for repeat (expected positive integer, got %d)", n))
 			}
-			return strings.Repeat(args[0].(string), n), nil
+			return uint(n), nil
+		},
+		Func: func(args ...any) (any, error) {
+			return strings.Repeat(args[0].(string), runtime.ToInt(args[1])), nil
 		},
 		Types: types(strings.Repeat),
 	},
diff --git a/builtin/builtin_test.go b/builtin/builtin_test.go
index a861d0fa..23273a24 100644
--- a/builtin/builtin_test.go
+++ b/builtin/builtin_test.go
@@ -260,9 +260,26 @@ func TestBuiltin_memory_limits(t *testing.T) {
 
 	for _, test := range tests {
 		t.Run(test.input, func(t *testing.T) {
-			_, err := expr.Eval(test.input, nil)
-			assert.Error(t, err)
-			assert.Contains(t, err.Error(), "memory budget exceeded")
+			timeout := make(chan bool, 1)
+			go func() {
+				time.Sleep(time.Second)
+				timeout <- true
+			}()
+
+			done := make(chan bool, 1)
+			go func() {
+				_, err := expr.Eval(test.input, nil)
+				assert.Error(t, err)
+				assert.Contains(t, err.Error(), "memory budget exceeded")
+				done <- true
+			}()
+
+			select {
+			case <-done:
+				// Success.
+			case <-timeout:
+				t.Fatal("timeout")
+			}
 		})
 	}
 }
diff --git a/compiler/compiler.go b/compiler/compiler.go
index f4bb3bd5..1f1c00c9 100644
--- a/compiler/compiler.go
+++ b/compiler/compiler.go
@@ -147,31 +147,31 @@ func (c *compiler) addVariable(name string) int {
 func (c *compiler) emitFunction(fn *builtin.Function, argsLen int) {
 	switch argsLen {
 	case 0:
-		c.emit(OpCall0, c.addFunction(fn))
+		c.emit(OpCall0, c.addFunction(fn.Name, fn.Func))
 	case 1:
-		c.emit(OpCall1, c.addFunction(fn))
+		c.emit(OpCall1, c.addFunction(fn.Name, fn.Func))
 	case 2:
-		c.emit(OpCall2, c.addFunction(fn))
+		c.emit(OpCall2, c.addFunction(fn.Name, fn.Func))
 	case 3:
-		c.emit(OpCall3, c.addFunction(fn))
+		c.emit(OpCall3, c.addFunction(fn.Name, fn.Func))
 	default:
-		c.emit(OpLoadFunc, c.addFunction(fn))
+		c.emit(OpLoadFunc, c.addFunction(fn.Name, fn.Func))
 		c.emit(OpCallN, argsLen)
 	}
 }
 
 // addFunction adds builtin.Function.Func to the program.functions and returns its index.
-func (c *compiler) addFunction(fn *builtin.Function) int {
+func (c *compiler) addFunction(name string, fn Function) int {
 	if fn == nil {
 		panic("function is nil")
 	}
-	if p, ok := c.functionsIndex[fn.Name]; ok {
+	if p, ok := c.functionsIndex[name]; ok {
 		return p
 	}
 	p := len(c.functions)
-	c.functions = append(c.functions, fn.Func)
-	c.functionsIndex[fn.Name] = p
-	c.debugInfo[fmt.Sprintf("func_%d", p)] = fn.Name
+	c.functions = append(c.functions, fn)
+	c.functionsIndex[name] = p
+	c.debugInfo[fmt.Sprintf("func_%d", p)] = name
 	return p
 }
 
@@ -904,6 +904,12 @@ func (c *compiler) BuiltinNode(node *ast.BuiltinNode) {
 		for _, arg := range node.Arguments {
 			c.compile(arg)
 		}
+
+		if f.ValidateArgs != nil {
+			c.emit(OpLoadFunc, c.addFunction("$_validate_args_"+f.Name, f.ValidateArgs))
+			c.emit(OpValidateArgs, len(node.Arguments))
+		}
+
 		if f.Fast != nil {
 			c.emit(OpCallBuiltin1, id)
 		} else if f.Func != nil {
diff --git a/vm/opcodes.go b/vm/opcodes.go
index 1106cd3f..57b84050 100644
--- a/vm/opcodes.go
+++ b/vm/opcodes.go
@@ -60,6 +60,7 @@ const (
 	OpCallFast
 	OpCallTyped
 	OpCallBuiltin1
+	OpValidateArgs
 	OpArray
 	OpMap
 	OpLen
diff --git a/vm/program.go b/vm/program.go
index 27b8f609..085b18a7 100644
--- a/vm/program.go
+++ b/vm/program.go
@@ -137,7 +137,7 @@ func (program *Program) DisassembleWriter(w io.Writer) {
 			constant("OpLoadMethod")
 
 		case OpLoadFunc:
-			argument("OpLoadFunc")
+			argumentWithInfo("OpLoadFunc", "func")
 
 		case OpLoadEnv:
 			code("OpLoadEnv")
@@ -278,6 +278,9 @@ func (program *Program) DisassembleWriter(w io.Writer) {
 		case OpCallBuiltin1:
 			builtinArg("OpCallBuiltin1")
 
+		case OpValidateArgs:
+			argument("OpValidateArgs")
+
 		case OpArray:
 			code("OpArray")
 
diff --git a/vm/vm.go b/vm/vm.go
index 20e1594f..fa2c7589 100644
--- a/vm/vm.go
+++ b/vm/vm.go
@@ -397,6 +397,14 @@ func (vm *VM) Run(program *Program, env any) (_ any, err error) {
 		case OpCallBuiltin1:
 			vm.push(builtin.Builtins[arg].Fast(vm.pop()))
 
+		case OpValidateArgs:
+			fn := vm.pop().(Function)
+			mem, err := fn(vm.stack[len(vm.stack)-arg:]...)
+			if err != nil {
+				panic(err)
+			}
+			vm.memGrow(mem.(uint))
+
 		case OpArray:
 			size := vm.pop().(int)
 			vm.memGrow(uint(size))