diff --git a/spec/RuleBuilderSpec.php b/spec/RuleBuilderSpec.php
index d742e30..2d1af37 100644
--- a/spec/RuleBuilderSpec.php
+++ b/spec/RuleBuilderSpec.php
@@ -14,13 +14,6 @@ function it_is_initializable()
         $this->shouldHaveType(RuleBuilder::class);
     }
 
-    function it_does_not_create_a_rule_without_constraints()
-    {
-        $this
-            ->shouldThrow(new \Exception('Can not create a rule without any requirement defined previously.'))
-            ->during('in', ['baz']);
-    }
-
     function it_chains_the_methods_for_building_a_rule()
     {
         $this->forbids(['foo', 'bar'])->shouldReturn($this);
diff --git a/src/Domain/Rule.php b/src/Domain/Rule.php
index a6d808d..5b97305 100644
--- a/src/Domain/Rule.php
+++ b/src/Domain/Rule.php
@@ -84,6 +84,10 @@ public function getUnusedRequirements(array $nodes): array
             return $this->matches($node);
         });
 
+        if ([] === $matchingNodes) {
+            return [];
+        }
+
         return array_filter($this->requirements, function (string $requirement) use ($matchingNodes) {
             if ($this->subject === $requirement) {
                 return false;
diff --git a/src/RuleBuilder.php b/src/RuleBuilder.php
index f9a7c96..c1b5368 100644
--- a/src/RuleBuilder.php
+++ b/src/RuleBuilder.php
@@ -52,10 +52,6 @@ public function discourages(array $requirements): RuleBuilder
 
     public function in(string $subject): RuleInterface
     {
-        if (empty($this->requirements)) {
-            throw new \Exception('Can not create a rule without any requirement defined previously.');
-        }
-
         if (null === $this->type) {
             throw new \Exception('Can not create a rule without any type defined previously.');
         }