diff --git a/composer.json b/composer.json
index b8ca9a54..c428b7ba 100644
--- a/composer.json
+++ b/composer.json
@@ -12,7 +12,7 @@
         "psr-4": {
             "React\\Promise\\": "src/"
         },
-        "files": ["src/functions.php"]
+        "files": ["src/functions_include.php"]
     },
     "extra": {
         "branch-alias": {
diff --git a/src/functions_include.php b/src/functions_include.php
new file mode 100644
index 00000000..c71decbf
--- /dev/null
+++ b/src/functions_include.php
@@ -0,0 +1,5 @@
+<?php
+
+if (!function_exists('React\Promise\resolve')) {
+    require __DIR__.'/functions.php';
+}