diff --git a/composer.json b/composer.json
index 0509248..00ac1b7 100644
--- a/composer.json
+++ b/composer.json
@@ -16,7 +16,7 @@
         "ext-curl": "*",
         "ext-json": "*",
         "doctrine/cache": "1.6.*",
-        "guzzlehttp/guzzle": "6.0",
+        "guzzlehttp/guzzle": "6.3.*",
         "lazyjsonmapper/lazyjsonmapper": "^1.6",
         "symfony/validator": "3.4.*",
         "doctrine/annotations": "1.6.*",
diff --git a/composer.lock b/composer.lock
index 29381f4..61c951d 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file",
         "This file is @generated automatically"
     ],
-    "content-hash": "fb7d2f0fa929696c1e3b8b70cc4eafe4",
+    "content-hash": "37c04715365723f98332d71aa2ee402e",
     "packages": [
         {
             "name": "corneltek/getoptionkit",
@@ -248,37 +248,40 @@
         },
         {
             "name": "guzzlehttp/guzzle",
-            "version": "6.0.0",
+            "version": "6.3.3",
             "source": {
                 "type": "git",
                 "url": "https://github.com/guzzle/guzzle.git",
-                "reference": "df897ae757ad329d2affc38ffb5bbce782b2b510"
+                "reference": "407b0cb880ace85c9b63c5f9551db498cb2d50ba"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/guzzle/guzzle/zipball/df897ae757ad329d2affc38ffb5bbce782b2b510",
-                "reference": "df897ae757ad329d2affc38ffb5bbce782b2b510",
+                "url": "https://api.github.com/repos/guzzle/guzzle/zipball/407b0cb880ace85c9b63c5f9551db498cb2d50ba",
+                "reference": "407b0cb880ace85c9b63c5f9551db498cb2d50ba",
                 "shasum": ""
             },
             "require": {
-                "guzzlehttp/promises": "^1.0.0",
-                "guzzlehttp/psr7": "^1.0.0",
-                "php": ">=5.5.0"
+                "guzzlehttp/promises": "^1.0",
+                "guzzlehttp/psr7": "^1.4",
+                "php": ">=5.5"
             },
             "require-dev": {
                 "ext-curl": "*",
-                "phpunit/phpunit": "^4.0",
+                "phpunit/phpunit": "^4.8.35 || ^5.7 || ^6.4 || ^7.0",
                 "psr/log": "^1.0"
             },
+            "suggest": {
+                "psr/log": "Required for using the Log middleware"
+            },
             "type": "library",
             "extra": {
                 "branch-alias": {
-                    "dev-master": "6.0-dev"
+                    "dev-master": "6.3-dev"
                 }
             },
             "autoload": {
                 "files": [
-                    "src/functions.php"
+                    "src/functions_include.php"
                 ],
                 "psr-4": {
                     "GuzzleHttp\\": "src/"
@@ -306,7 +309,7 @@
                 "rest",
                 "web service"
             ],
-            "time": "2015-05-26T18:22:06+00:00"
+            "time": "2018-04-22T15:46:56+00:00"
         },
         {
             "name": "guzzlehttp/promises",
@@ -4412,12 +4415,12 @@
         }
     ],
     "aliases": [],
-    "minimum-stability": "stable",
+    "minimum-stability": "dev",
     "stability-flags": [],
-    "prefer-stable": false,
+    "prefer-stable": true,
     "prefer-lowest": false,
     "platform": {
-        "php": ">=7.0",
+        "php": ">=7.1",
         "ext-curl": "*",
         "ext-json": "*"
     },