diff --git a/src/interfaces/maybe.interface.ts b/src/interfaces/maybe.interface.ts
index 42d8580..1032c6a 100644
--- a/src/interfaces/maybe.interface.ts
+++ b/src/interfaces/maybe.interface.ts
@@ -7,7 +7,7 @@ export interface IMaybePattern<TIn, TOut> {
   /**
    * Function to handle when a value exists.
    */
-  some(val: TIn): TOut
+  some(val: NonNullable<TIn>): TOut
 
   /**
    * Function to handle when a value is undefined.
@@ -22,12 +22,12 @@ export interface IMaybe<T> extends IMonad<T> {
   /**
    * Unwrap a Maybe with a default value
    */
-  valueOr(val: T): T
+  valueOr(val: NonNullable<T>): NonNullable<T>
 
   /**
    * Unwrap a Maybe with a default computed value
    */
-  valueOrCompute(f: () => T): T
+  valueOrCompute(f: () => NonNullable<T>): NonNullable<T>
 
   /**
    * Execute functions with side-effects.
@@ -42,7 +42,7 @@ export interface IMaybe<T> extends IMonad<T> {
   /**
    * Execute a function with side-effects when maybe is a some.
    */
-  tapSome(f: (val: T) => void): void
+  tapSome(f: (val: NonNullable<T>) => void): void
 
   /**
    * Unwrap and apply MaybePattern functions
@@ -52,12 +52,12 @@ export interface IMaybe<T> extends IMonad<T> {
   /**
    * Combine multiple maybe
    */
-  map<R>(f: (t: T) => R): IMaybe<R>
+  map<R>(f: (t: NonNullable<T>) => R): IMaybe<R>
 
   /**
    * Combine multiple maybe
    */
-  flatMap<R>(f: (t: T) => IMaybe<R>): IMaybe<R>
+  flatMap<R>(f: (t: NonNullable<T>) => IMaybe<R>): IMaybe<R>
 
   // tslint:disable-next-line:readonly-array
   of(x?: T, ...args: any[]): IMaybe<T>
diff --git a/src/monads/maybe.ts b/src/monads/maybe.ts
index e34ff6c..bde440d 100644
--- a/src/monads/maybe.ts
+++ b/src/monads/maybe.ts
@@ -3,13 +3,13 @@ import { IMaybe, IMaybePattern } from "../interfaces"
 export function maybe<T>(value?: T): IMaybe<T> {
   return {
     of: (x) => maybe(x),
-    valueOr: (val: T) => value === null || value === undefined ? val : value,
-    valueOrCompute: (f: () => T) => value === null || value === undefined ? f() : value,
-    tap: (obj: Partial<IMaybePattern<T, void>>) => value === null || value === undefined ? obj.none && obj.none() : obj.some && obj.some(value),
+    valueOr: (val: NonNullable<T>) => value === null || value === undefined ? val : value as NonNullable<T>,
+    valueOrCompute: (f: () => NonNullable<T>) => value === null || value === undefined ? f() : value as NonNullable<T>,
+    tap: (obj: Partial<IMaybePattern<T, void>>) => value === null || value === undefined ? obj.none && obj.none() : obj.some && obj.some(value as  NonNullable<T>),
     tapNone: (f: () => void) => (value === null || value === undefined) && f(),
-    tapSome: (f: (val: T) => void) => value !== null && value !== undefined && f(value),
-    match: <R>(pattern: IMaybePattern<T, R>) => value === null || value === undefined ? pattern.none() : pattern.some(value),
-    map: <R>(f: (t: T) => R) => value === null || value === undefined ? maybe<R>() : maybe<R>(f(value)),
-    flatMap: <R>(f: (d: T) => IMaybe<R>) => value === null || value === undefined ? maybe<R>() : f(value)
+    tapSome: (f: (val: NonNullable<T>) => void) => value !== null && value !== undefined && f(value as NonNullable<T>),
+    match: <R>(pattern: IMaybePattern<T, R>) => value === null || value === undefined ? pattern.none() : pattern.some(value as  NonNullable<T>),
+    map: <R>(f: (t: NonNullable<T>) => R) => value === null || value === undefined ? maybe<R>() : maybe<R>(f(value as NonNullable<T>)),
+    flatMap: <R>(f: (d:  NonNullable<T>) => IMaybe<R>) => value === null || value === undefined ? maybe<R>() : f(value as  NonNullable<T>)
   }
 }
\ No newline at end of file
diff --git a/test/monads/maybe.spec.ts b/test/monads/maybe.spec.ts
index a36bf8b..90de6c8 100644
--- a/test/monads/maybe.spec.ts
+++ b/test/monads/maybe.spec.ts
@@ -3,35 +3,35 @@ import { maybe } from "../../src"
 describe('Maybe', () => {
   describe('when returning a value by default', () => {
     it('should handle "none" case', () => {
-      const sut: string | undefined = undefined
+      const sut = undefined as string | undefined
       const maybeAString = maybe(sut).valueOr('default output')
 
       expect(maybeAString).toEqual('default output')
     })
 
     it('should handle "some" case', () => {
-      const sut: string | undefined = 'actual input'
+      const sut = 'actual input' as string | undefined
       const maybeAString = maybe(sut).valueOr('default output')
 
       expect(maybeAString).toEqual('actual input')
     })
 
     it('should handle "some" case when input is null', () => {
-      const sut: string | undefined | null = null
+      const sut = null as string | undefined | null
       const maybeAString = maybe(sut).valueOr('default output')
 
       expect(maybeAString).toEqual('default output')
     })
 
     it('should handle "some" case when input is ""', () => {
-      const sut: string | undefined | null = ''
+      const sut = '' as string | undefined | null
       const maybeAString = maybe(sut).valueOr('fallback')
 
       expect(maybeAString).toEqual('')
     })
 
     it('should handle "some" case when input is 0', () => {
-      const sut: number | undefined | null = 0
+      const sut = 0 as number | undefined | null
       const maybeAString = maybe(sut).valueOr(10)
 
       expect(maybeAString).toEqual(0)
@@ -40,7 +40,7 @@ describe('Maybe', () => {
 
   describe('when returning a value by computation', () => {
     it('should handle "none" case', () => {
-      const sut: string | undefined = undefined
+      const sut = undefined as string | undefined
       const maybeAString = maybe(sut).valueOrCompute(() => 'default output')
 
       expect(maybeAString).toEqual('default output')
@@ -54,21 +54,21 @@ describe('Maybe', () => {
     })
 
     it('should handle "some" case when input is null', () => {
-      const sut: string | undefined = null
+      const sut = null as string | null
       const maybeAString = maybe(sut).valueOrCompute(() => 'fallback')
 
       expect(maybeAString).toEqual('fallback')
     })
 
     it('should handle "some" case when input is ""', () => {
-      const sut: string | undefined = ''
+      const sut = '' as string | undefined
       const maybeAString = maybe(sut).valueOrCompute(() => 'fallback')
 
       expect(maybeAString).toEqual('')
     })
 
     it('should handle "some" case when input is 0', () => {
-      const sut: number | undefined = 0
+      const sut = 0 as number | undefined
       const maybeAString = maybe(sut).valueOrCompute(() => 10)
 
       expect(maybeAString).toEqual(0)
@@ -77,7 +77,7 @@ describe('Maybe', () => {
 
   describe('when returning from a match operation', () => {
     it('should handle "none" case', () => {
-      const sut: string | undefined = undefined
+      const sut = undefined as string | undefined
       const maybeAMappedString = maybe(sut)
         .match({
           none: () => 'fallback',
@@ -88,7 +88,7 @@ describe('Maybe', () => {
     })
 
     it('should handle "some" case', () => {
-      const sut: string | undefined = 'existing value'
+      const sut = 'existing value' as string | undefined
       const maybeAMappedString = maybe(sut)
         .match({
           none: () => 'fallback',
@@ -102,8 +102,8 @@ describe('Maybe', () => {
   describe('when performing side-effect operations', () => {
     it('should handle "none" case', () => {
       // tslint:disable-next-line:no-let
-      let sideEffectStore: string
-      const sut: string | undefined = undefined
+      let sideEffectStore = ''
+      const sut = undefined as string | undefined
 
       maybe(sut)
         .tap({
@@ -118,8 +118,8 @@ describe('Maybe', () => {
 
     it('should handle "some" case', () => {
       // tslint:disable-next-line:no-let
-      let sideEffectStore: string
-      const sut: string | undefined = 'existing value'
+      let sideEffectStore = ''
+      const sut = 'existing value' as string | undefined
 
       maybe(sut)
         .tap({
@@ -139,7 +139,7 @@ describe('Maybe', () => {
     }
 
     it('should handle valid input', () => {
-      const sut: string | undefined = 'initial input'
+      const sut = 'initial input' as string | undefined
 
       const maybeSomeString = maybe(sut)
         .map(_str => getUserService<string>('initial input mapped'))
@@ -163,7 +163,7 @@ describe('Maybe', () => {
     })
 
     it('should handle undefined input', () => {
-      const sut: string | undefined = undefined
+      const sut = undefined as string | undefined
 
       const maybeSomeString = maybe(sut)
         .map(_str => getUserService<string>('initial input mapped'))
@@ -187,7 +187,7 @@ describe('Maybe', () => {
     })
 
     it('should handle input of 0', () => {
-      const sut: number | undefined = 0
+      const sut = 0 as number | undefined
 
       const maybeSomeString = maybe(sut)
         .map(_str => getUserService<string>('initial input mapped'))
@@ -211,7 +211,7 @@ describe('Maybe', () => {
     })
 
     it('should handle input of ""', () => {
-      const sut: string | undefined = ''
+      const sut = '' as string | undefined
 
       const maybeSomeString = maybe(sut)
         .map(_str => getUserService<string>('initial input mapped'))
@@ -237,8 +237,8 @@ describe('Maybe', () => {
 
   describe('when flatMapping', () => {
     it('should handle "none" case', () => {
-      const sut: string | undefined = undefined
-      const nsut: number | undefined = undefined
+      const sut = undefined as string | undefined
+      const nsut = undefined as number | undefined
 
       const maybeSomeNumber = maybe(sut)
         .flatMap(() => maybe(nsut))
@@ -248,8 +248,8 @@ describe('Maybe', () => {
     })
 
     it('should handle "some" case', () => {
-      const sut: string | undefined = 'initial'
-      const nsut: number | undefined = 20
+      const sut = 'initial' as string | undefined
+      const nsut = 20 as number | undefined
 
       const maybeSomeNumber = maybe(sut)
         .flatMap(() => maybe(nsut))
@@ -261,7 +261,7 @@ describe('Maybe', () => {
 
   describe('when getting monadic unit', () => {
     it('should get value', () => {
-      const sut: string | undefined = undefined
+      const sut = undefined as string | undefined
 
       const maybeSomeNumber = maybe(sut)
         .of('ok')
@@ -273,7 +273,7 @@ describe('Maybe', () => {
 
   describe('when tapSome', () => {
     it('should work', () => {
-      const sut: string | undefined = 'abc'
+      const sut = 'abc' as string | undefined
 
       expect.assertions(1)
       maybe(sut).tapSome(a => expect(a).toEqual('abc'))
@@ -283,7 +283,7 @@ describe('Maybe', () => {
 
   describe('when tapNone', () => {
     it('should work', () => {
-      const sut: string | undefined = undefined
+      const sut = undefined as string | undefined
 
       expect.assertions(1)
       maybe(sut).tapNone(() => expect(1).toEqual(1))
diff --git a/test/tsconfig.json b/test/tsconfig.json
new file mode 100644
index 0000000..ad35aba
--- /dev/null
+++ b/test/tsconfig.json
@@ -0,0 +1,25 @@
+{
+  "compilerOptions": {
+    "target": "es5",
+    "module": "commonjs",
+    "moduleResolution": "node",
+    "lib": ["es2015", "dom"],
+    "isolatedModules": false,
+    "experimentalDecorators": true,
+    "emitDecoratorMetadata": true,
+    "noImplicitAny": true,
+    "noImplicitUseStrict": false,
+    "noEmitHelpers": false,
+    "noEmit": true,
+    "noLib": false,
+    "noUnusedLocals": true,
+    "noEmitOnError": true,
+    "allowSyntheticDefaultImports": false,
+    "skipLibCheck": true,
+    "skipDefaultLibCheck": true,
+    "strict": true,
+    "strictNullChecks": true,
+    "strictFunctionTypes": true,
+    "forceConsistentCasingInFileNames": true
+  }
+}
\ No newline at end of file