diff --git a/src/collections_methods.c b/src/collections_methods.c
index 1990ea2..068d728 100644
--- a/src/collections_methods.c
+++ b/src/collections_methods.c
@@ -1641,7 +1641,53 @@ PHP_METHOD(Collection, groupBy)
 
 PHP_METHOD(Collection, groupByTo)
 {
-    
+    zval* dest;
+    zend_fcall_info fci;
+    zend_fcall_info_cache fcc;
+    ZEND_PARSE_PARAMETERS_START(2, 2)
+        Z_PARAM_OBJECT_OF_CLASS(dest, collections_collection_ce)
+        Z_PARAM_FUNC(fci, fcc)
+    ZEND_PARSE_PARAMETERS_END();
+    zend_array* current = COLLECTION_FETCH_CURRENT();
+    zend_array* dest_arr = COLLECTION_FETCH(dest);
+    SEPARATE_COLLECTION(dest_arr, dest);
+    zend_bool packed = HT_IS_PACKED(current);
+    INIT_FCI(&fci, 2);
+    ZEND_HASH_FOREACH_BUCKET(current, Bucket* bucket)
+        CALLBACK_KEYVAL_INVOKE(params, bucket);
+        zval* key;
+        zval* value;
+        if (IS_PAIR(retval))
+        {
+            key = PAIR_FIRST(Z_OBJ(retval));
+            value = PAIR_SECOND(Z_OBJ(retval));
+        }
+        else
+        {
+            key = &retval;
+            value = &bucket->val;
+        }
+        Z_TRY_ADDREF_P(value);
+        zend_array* group = array_group_fetch(dest_arr, key);
+        if (UNEXPECTED(group == NULL))
+        {
+            continue;
+        }
+        if (bucket->key)
+        {
+            zend_hash_add(group, bucket->key, value);
+        }
+        else if (packed)
+        {
+            zend_hash_next_index_insert(group, value);
+        }
+        else
+        {
+            zend_hash_index_add(group, bucket->h, value);
+        }
+        zval_ptr_dtor(&retval);
+    ZEND_HASH_FOREACH_END();
+    RETVAL_NEW_COLLECTION(dest_arr);
 }
 
 PHP_METHOD(Collection, indexOf)
diff --git a/tests/050-group-by.phpt b/tests/050-group-by.phpt
index 3d75e04..4cffb0b 100644
--- a/tests/050-group-by.phpt
+++ b/tests/050-group-by.phpt
@@ -1,5 +1,5 @@
 --TEST--
-Test Collection::groupBy().
+Test Collection::groupBy() and Collection::groupByTo().
 --FILE--
 <?php
 $collection = Collection::init([
@@ -27,18 +27,22 @@ if ($collection1->toArray() != $array) {
 }
 
 $collection = Collection::init([7, 2, 9, 4, 1, 0]);
-$collection1 = $collection->groupBy(function ($value, $key) {
-    if ($key % 2) {
-        return 'odd_idx';
+$collection1 = Collection::init(['foo' => 'bar']);
+$collection2 = $collection->groupByTo($collection1,
+    function ($value, $key) {
+        if ($key % 2) {
+            return 'odd_idx';
+        }
+        return 'even_idx';
     }
-    return 'even_idx';
-});
+);
 $array = [
+    'foo' => 'bar',
     'odd_idx' => [2, 4, 0],
     'even_idx' => [7, 9, 1]
 ];
-if ($collection1->toArray() != $array) {
-    echo 'Collection::groupBy() failed.', PHP_EOL;
+if ($collection2->toArray() != $array) {
+    echo 'Collection::groupByTo() failed.', PHP_EOL;
 }
 ?>
 --EXPECT--