diff --git a/src/Organization.php b/src/Organization.php
index 0660bd4..7168d50 100644
--- a/src/Organization.php
+++ b/src/Organization.php
@@ -71,7 +71,7 @@ public function format(bool $separator = true): string
      */
     public function valid(): bool
     {
-        if (!preg_match("/^\d{6}[\-\/]?\d{4}+$/", $this->orgNo)) {
+        if (!preg_match('/^\d{6}-?\d{4}$/', $this->orgNo)) {
             return false;
         }
 
diff --git a/tests/SwedishEntityTest.php b/tests/SwedishEntityTest.php
index a69010b..4f2d4d7 100644
--- a/tests/SwedishEntityTest.php
+++ b/tests/SwedishEntityTest.php
@@ -133,6 +133,7 @@ public function testInvalidCompanies()
         $this->assertFalse((new Organization('556016-0681'))->valid());
         $this->assertFalse((new Organization('556103-4250'))->valid());
         $this->assertFalse((new Organization('5561034250'))->valid());
+        $this->assertFalse((new Organization('556103/4250'))->valid());
     }
 
     /** @test */