diff --git a/src/Incoming/Structure/StructureFactory.php b/src/Incoming/Structure/StructureFactory.php
index 329d0b7..50cd892 100644
--- a/src/Incoming/Structure/StructureFactory.php
+++ b/src/Incoming/Structure/StructureFactory.php
@@ -81,7 +81,7 @@ protected static function buildFromTraversable(Traversable $data)
 
         // Traverse through the data, but only check the first item's key
         foreach ($data as $key => &$val) {
-            $is_map = !is_int($key);
+            $is_map = $is_map || !is_int($key);
 
             $val = self::attemptBuildTraversableLike($val);
         }
diff --git a/tests/Incoming/Test/Structure/StructureFactoryTest.php b/tests/Incoming/Test/Structure/StructureFactoryTest.php
index 13f2338..cfdad4f 100644
--- a/tests/Incoming/Test/Structure/StructureFactoryTest.php
+++ b/tests/Incoming/Test/Structure/StructureFactoryTest.php
@@ -122,4 +122,19 @@ public function testBuildWithInvalidStructuralType()
 
         $structure = (new StructureFactory)->build($data);
     }
+
+    /**
+     * @link https://github.com/Rican7/incoming/pull/3
+     */
+    public function testBuildWithTraversableAndMixedKeys()
+    {
+        $data = new ArrayIterator([
+            'name' => 'markus',
+            0 => 'a crazy mixed-in key'
+        ]);
+
+        $structure = (new StructureFactory)->build($data);
+
+        $this->assertTrue($structure instanceof Map);
+    }
 }