diff --git a/src/Composer/DependencyResolver/Solver.php b/src/Composer/DependencyResolver/Solver.php
index c0a09f16b..2ad3965fe 100644
--- a/src/Composer/DependencyResolver/Solver.php
+++ b/src/Composer/DependencyResolver/Solver.php
@@ -53,7 +53,8 @@ class Solver
     {
         $decisionStart = count($this->decisions) - 1;
 
-        for ($ruleIndex = 0; $ruleIndex < count($this->rules); $ruleIndex++) {
+        $rulesCount = count($this->rules);
+        for ($ruleIndex = 0; $ruleIndex < $rulesCount; $ruleIndex++) {
             $rule = $this->rules->ruleById($ruleIndex);
 
             if (!$rule->isAssertion() || $rule->isDisabled()) {