diff --git a/src/Ginq/Iterator/ZipIterator.php b/src/Ginq/Iterator/ZipIterator.php
index 66f5c7b..d1bd479 100644
--- a/src/Ginq/Iterator/ZipIterator.php
+++ b/src/Ginq/Iterator/ZipIterator.php
@@ -100,12 +100,14 @@ public function valid()
 
     protected function fetch()
     {
-        $v0 = $this->it0->current();
-        $v1 = $this->it1->current();
-        $k0 = $this->it0->key();
-        $k1 = $this->it1->key();
-        $this->v = $this->valueJoinSelector->select($v0, $v1, $k0, $k1);
-        $this->k = $this->keyJoinSelector->select($v0, $v1, $k0, $k1);
+        if ($this->valid()) {
+            $v0 = $this->it0->current();
+            $v1 = $this->it1->current();
+            $k0 = $this->it0->key();
+            $k1 = $this->it1->key();
+            $this->v = $this->valueJoinSelector->select($v0, $v1, $k0, $k1);
+            $this->k = $this->keyJoinSelector->select($v0, $v1, $k0, $k1);
+        }
     }
 }