diff --git a/bin/composer b/bin/composer
index 88566e170..0664e04ce 100755
--- a/bin/composer
+++ b/bin/composer
@@ -45,6 +45,10 @@ if (function_exists('ini_set')) {
     if ($memoryLimit != -1 && $memoryInBytes($memoryLimit) < 1024 * 1024 * 1536) {
         @ini_set('memory_limit', '1536M');
     }
+    // Set user defined memory limit
+    if ($memoryLimit = getenv('COMPOSER_MEMORY_LIMIT')) {
+        @ini_set('memory_limit', $memoryLimit);
+    }
     unset($memoryInBytes, $memoryLimit);
 }
 
diff --git a/doc/03-cli.md b/doc/03-cli.md
index 4880d5406..04ae1d0ae 100644
--- a/doc/03-cli.md
+++ b/doc/03-cli.md
@@ -909,6 +909,10 @@ If set to 1, this env disables the warning about running commands as root/super
 It also disables automatic clearing of sudo sessions, so you should really only set this
 if you use Composer as super user at all times like in docker containers.
 
+### COMPOSER_MEMORY_LIMIT
+
+If set, the value is used as php's memory_limit.
+
 ### COMPOSER_MIRROR_PATH_REPOS
 
 If set to 1, this env changes the default path repository strategy to `mirror` instead