diff --git a/src/JWT.php b/src/JWT.php
index 37a9e0e6..e8fc901f 100644
--- a/src/JWT.php
+++ b/src/JWT.php
@@ -152,30 +152,46 @@ public static function decode(
 
         // Check the nbf if it is defined. This is the time that the
         // token can actually be used. If it's not yet that time, abort.
-        if (isset($payload->nbf) && floor($payload->nbf) > ($timestamp + static::$leeway)) {
-            $ex = new BeforeValidException(
-                'Cannot handle token with nbf prior to ' . \date(DateTime::ATOM, (int) floor($payload->nbf))
-            );
-            $ex->setPayload($payload);
-            throw $ex;
+        if (isset($payload->nbf)) {
+            if (!\is_int($payload->nbf)) {
+                throw new UnexpectedValueException('The property nbf must be of type integer.');
+            }
+            if (floor($payload->nbf) > ($timestamp + static::$leeway)) {
+                $ex = new BeforeValidException(
+                    'Cannot handle token with nbf prior to ' . \date(DateTime::ATOM, (int) floor($payload->nbf))
+                );
+                $ex->setPayload($payload);
+                throw $ex;
+            }
         }
 
         // Check that this token has been created before 'now'. This prevents
         // using tokens that have been created for later use (and haven't
         // correctly used the nbf claim).
-        if (!isset($payload->nbf) && isset($payload->iat) && floor($payload->iat) > ($timestamp + static::$leeway)) {
-            $ex = new BeforeValidException(
-                'Cannot handle token with iat prior to ' . \date(DateTime::ATOM, (int) floor($payload->iat))
-            );
-            $ex->setPayload($payload);
-            throw $ex;
+        if (isset($payload->iat)) {
+            if (!\is_int($payload->iat)) {
+                throw new UnexpectedValueException('The property iat must be of type integer.');
+            }
+            if (floor($payload->iat) > ($timestamp + static::$leeway)) {
+                $ex = new BeforeValidException(
+                    'Cannot handle token with iat prior to ' . \date(DateTime::ATOM, (int) floor($payload->iat))
+                );
+                $ex->setPayload($payload);
+                throw $ex;
+            }
         }
 
         // Check if this token has expired.
-        if (isset($payload->exp) && ($timestamp - static::$leeway) >= $payload->exp) {
-            $ex = new ExpiredException('Expired token');
-            $ex->setPayload($payload);
-            throw $ex;
+        if (isset($payload->exp)) {
+            if (!\is_int($payload->exp)) {
+                throw new UnexpectedValueException('The property exp must be of type integer.');
+            }
+          
+            if (($timestamp - static::$leeway) >= $payload->exp) {
+                $ex = new ExpiredException('Expired token');
+                $ex->setPayload($payload);
+                throw $ex;
+            }
         }
 
         return $payload;
@@ -211,6 +227,15 @@ public static function encode(
         if ($keyId !== null) {
             $header['kid'] = $keyId;
         }
+        if (isset($payload['nbf']) && !\is_int($payload['nbf'])) {
+            throw new UnexpectedValueException('The property nbf must be an integer containing a unix timestamp.');
+        }
+        if (isset($payload['iat']) && !\is_int($payload['iat'])) {
+            throw new UnexpectedValueException('The property nbf must be an integer containing a unix timestamp.');
+        }
+        if (isset($payload['exp']) && !\is_int($payload['exp'])) {
+            throw new UnexpectedValueException('The property exp must be an integer containing a unix timestamp.');
+        }
         $segments = [];
         $segments[] = static::urlsafeB64Encode((string) static::jsonEncode($header));
         $segments[] = static::urlsafeB64Encode((string) static::jsonEncode($payload));
diff --git a/tests/JWTTest.php b/tests/JWTTest.php
index d09d43e3..4ca53f6a 100644
--- a/tests/JWTTest.php
+++ b/tests/JWTTest.php
@@ -546,4 +546,58 @@ public function testAdditionalHeaderOverrides()
         $this->assertEquals('my_key_id', $headers->kid, 'key param not overridden');
         $this->assertEquals('HS256', $headers->alg, 'alg param not overridden');
     }
+
+    public function testEncodeExpectsIntegerIat()
+    {
+        $this->expectException(UnexpectedValueException::class);
+        $payload = [
+            'iat' => 'abc',
+        ];
+        JWT::encode($payload, 'my_key', 'HS256');
+    }
+
+    public function testDecodeExpectsIntegerIat()
+    {
+        $this->expectException(UnexpectedValueException::class);
+        JWT::decode(
+            'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMzM3IiwibmFtZSI6IkpvaG4gU25vdyIsImlhdCI6InRlc3QifQ.B8cbURVQAPay3-Ep0DAm1Ji2rhij-hxfNA5PIDarf5o',
+            new Key('secret', 'HS256')
+        );
+    }
+
+    public function testEncodeExpectsIntegerNbf()
+    {
+        $this->expectException(UnexpectedValueException::class);
+        $payload = [
+            'nbf' => 'abc',
+        ];
+        JWT::encode($payload, 'my_key', 'HS256');
+    }
+
+    public function testDecodeExpectsIntegerNbf()
+    {
+        $this->expectException(UnexpectedValueException::class);
+        JWT::decode(
+            'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMzM3IiwibmFtZSI6IkpvaG4gU25vdyIsIm5iZiI6InRlc3QifQ.9KdFz3ktQoPO5QFG3E7J86PEuw5Vmx0VPrUKszP7DDs',
+            new Key('secret', 'HS256')
+        );
+    }
+
+    public function testEncodeExpectsIntegerExp()
+    {
+        $this->expectException(UnexpectedValueException::class);
+        $payload = [
+            'exp' => 'abc',
+        ];
+        JWT::encode($payload, 'my_key', 'HS256');
+    }
+
+    public function testDecodeExpectsIntegerExp()
+    {
+        $this->expectException(UnexpectedValueException::class);
+        JWT::decode(
+            'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMzM3IiwibmFtZSI6IkpvaG4gU25vdyIsImV4cCI6InRlc3QifQ.LXevvGvchI3PTBZo9jZ5-4d0OvONVU-_8Tbg_22-PTo',
+            new Key('secret', 'HS256')
+        );
+    }
 }