diff --git a/src/types/modifiers.ts b/src/types/modifiers.ts
index 5b14675f1..1cc5665b4 100644
--- a/src/types/modifiers.ts
+++ b/src/types/modifiers.ts
@@ -1,4 +1,4 @@
-import {isPlainObject, invariant} from "../utils/utils";
+import {isPlainObject, invariant, isObject} from "../utils/utils";
 import {isObservable} from "../api/isobservable";
 import {extendObservableHelper} from "../api/extendobservable";
 import {createObservableArray} from "../types/observablearray";
@@ -12,6 +12,26 @@ export enum ValueMode {
 	Flat       // If the value is an plain object, it will be made reactive, and so will all its future children.
 }
 
+export interface IModifierWrapper {
+	mobxModifier: ValueMode;
+	value: any;
+}
+
+function withModifier(modifier: ValueMode, value: any): IModifierWrapper {
+	assertUnwrapped(value, "Modifiers are not allowed to be nested");
+	return {
+		mobxModifier: modifier,
+		value
+	};
+}
+
+export function getModifier(value: any): ValueMode {
+	if (value) { // works for both objects and functions
+		return (value.mobxModifier as ValueMode) || null;
+	}
+	return null;
+}
+
 
 /**
 	* Can be used in combination with makeReactive / extendReactive.
@@ -23,8 +43,9 @@ export enum ValueMode {
 export function asReference<T>(value: T): T {
 	// unsound typecast, but in combination with makeReactive, the end result should be of the correct type this way
 	// e.g: makeReactive({ x : asReference(number)}) -> { x : number }
-	return <T><any> new AsReference(value);
+	return withModifier(ValueMode.Reference, value) as any as T;
 }
+(asReference as any).mobxModifier = ValueMode.Reference;
 
 /**
 	* Can be used in combination with makeReactive / extendReactive.
@@ -37,8 +58,9 @@ export function asReference<T>(value: T): T {
 	* @param value initial value of the reactive property that is being defined.
 	*/
 export function asStructure<T>(value: T): T {
-	return <T><any>new AsStructure(value);
+	return withModifier(ValueMode.Structure, value) as any as T;
 }
+(asStructure as any).mobxModifier = ValueMode.Structure;
 
 /**
 	* Can be used in combination with makeReactive / extendReactive.
@@ -46,26 +68,9 @@ export function asStructure<T>(value: T): T {
 	* children will not automatically be made reactive as well.
 	*/
 export function asFlat<T>(value: T): T {
-	return <T><any> new AsFlat(value);
-}
-
-export class AsReference {
-	constructor(public value: any) {
-		assertUnwrapped(value, "Modifiers are not allowed to be nested");
-	}
-}
-
-export class AsStructure {
-	constructor(public value: any) {
-		assertUnwrapped(value, "Modifiers are not allowed to be nested");
-	}
-}
-
-export class AsFlat {
-	constructor(public value: any) {
-		assertUnwrapped(value, "Modifiers are not allowed to be nested");
-	}
+	return withModifier(ValueMode.Flat, value) as any as T;
 }
+(asFlat as any).mobxModifier = ValueMode.Flat;
 
 export function asMap(): ObservableMap<any>;
 export function asMap<T>(): ObservableMap<T>;
@@ -76,24 +81,18 @@ export function asMap(data?, modifierFunc?): ObservableMap<any> {
 }
 
 export function getValueModeFromValue(value: any, defaultMode: ValueMode): [ValueMode, any] {
-	if (value instanceof AsReference)
-		return [ValueMode.Reference, value.value];
-	if (value instanceof AsStructure)
-		return [ValueMode.Structure, value.value];
-	if (value instanceof AsFlat)
-		return [ValueMode.Flat, value.value];
+	const mode = getModifier(value);
+	if (mode)
+		return [mode, value.value];
 	return [defaultMode, value];
 }
 
 export function getValueModeFromModifierFunc(func?: Function): ValueMode {
-	if (func === asReference)
-		return ValueMode.Reference;
-	else if (func === asStructure)
-		return ValueMode.Structure;
-	else if (func === asFlat)
-		return ValueMode.Flat;
-	invariant(func === undefined, "Cannot determine value mode from function. Please pass in one of these: mobx.asReference, mobx.asStructure or mobx.asFlat, got: " + func);
-	return ValueMode.Recursive;
+	if (func === undefined)
+		return ValueMode.Recursive;
+	const mod = getModifier(func);
+	invariant(mod !== null, "Cannot determine value mode from function. Please pass in one of these: mobx.asReference, mobx.asStructure or mobx.asFlat, got: " + func);
+	return mod;
 }
 
 
@@ -128,6 +127,6 @@ export function makeChildObservable(value, parentMode: ValueMode, name?: string)
 }
 
 export function assertUnwrapped(value, message) {
-	if (value instanceof AsReference || value instanceof AsStructure || value instanceof AsFlat)
+	if (getModifier(value) !== null)
 		throw new Error(`[mobx] asStructure / asReference / asFlat cannot be used here. ${message}`);
 }
diff --git a/src/types/observableobject.ts b/src/types/observableobject.ts
index 05ec108ab..1af19f87a 100644
--- a/src/types/observableobject.ts
+++ b/src/types/observableobject.ts
@@ -1,7 +1,7 @@
-import {isObservableValue, ObservableValue, UNCHANGED} from "./observablevalue";
+import {ObservableValue, UNCHANGED} from "./observablevalue";
 import {isComputedValue, ComputedValue} from "../core/computedvalue";
 import {isAction} from "../api/action";
-import {ValueMode, AsStructure} from "./modifiers";
+import {ValueMode, getModifier} from "./modifiers";
 import {createInstanceofPredicate, isObject, Lambda, getNextId, invariant, assertPropertyConfigurable, isPlainObject, addHiddenFinalProp} from "../utils/utils";
 import {runLazyInitializers} from "../utils/decorators";
 import {hasInterceptors, IInterceptable, registerInterceptor, interceptChange} from "./intercept-utils";
@@ -101,7 +101,7 @@ export function defineObservableProperty(adm: ObservableObjectAdministration, pr
 		// TODO: add warning in 2.6, see https://github.com/mobxjs/mobx/issues/421
 		// TODO: remove in 3.0
 		observable = new ComputedValue(newValue, adm.target, false, name, setter);
-	} else if (newValue instanceof AsStructure && typeof newValue.value === "function" && newValue.value.length === 0) {
+	} else if (getModifier(newValue) === ValueMode.Structure && typeof newValue.value === "function" && newValue.value.length === 0) {
 		observable = new ComputedValue(newValue.value, adm.target, true, name, setter);
 	} else {
 		isComputed = false;
diff --git a/src/utils/utils.ts b/src/utils/utils.ts
index c1b3162d4..33003deb8 100644
--- a/src/utils/utils.ts
+++ b/src/utils/utils.ts
@@ -167,6 +167,7 @@ export function deepEquals(a, b) {
 }
 
 export function createInstanceofPredicate<T>(name: string, clazz: new (...args:any[]) => T): (x: any) => x is T {
+	// TODO: this is quite a slow aproach, find something faster?
 	const propName = "isMobX" + name;
 	clazz.prototype[propName] = true;
 	return function (x) {