diff --git a/CHANGES.rst b/CHANGES.rst
index 7ee75a6a7..5668e549d 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -5,6 +5,9 @@ Version 3.2.0
 
 Unreleased
 
+- Fix ``unique()`` when chained with `reject()` or `rejectattr()`
+  :issue:`1781`
+
 
 Version 3.1.2
 -------------
diff --git a/src/jinja2/filters.py b/src/jinja2/filters.py
index ed07c4c0e..60dc1046b 100644
--- a/src/jinja2/filters.py
+++ b/src/jinja2/filters.py
@@ -410,7 +410,7 @@ def do_sort(
 
 
 @pass_environment
-def do_unique(
+def sync_do_unique(
     environment: "Environment",
     value: "t.Iterable[V]",
     case_sensitive: bool = False,
@@ -442,6 +442,18 @@ def do_unique(
             yield item
 
 
+@async_variant(sync_do_unique)  # type: ignore
+async def do_unique(
+    environment: "Environment",
+    value: "t.Union[t.AsyncIterable[V], t.Iterable[V]]",
+    case_sensitive: bool = False,
+    attribute: t.Optional[t.Union[str, int]] = None,
+) -> "t.Iterator[V]":
+    return sync_do_unique(
+        environment, await auto_to_list(value), case_sensitive, attribute
+    )
+
+
 def _min_or_max(
     environment: "Environment",
     value: "t.Iterable[V]",
diff --git a/tests/test_async_filters.py b/tests/test_async_filters.py
index f5b2627ad..b8aadf509 100644
--- a/tests/test_async_filters.py
+++ b/tests/test_async_filters.py
@@ -245,6 +245,13 @@ def test_slice(env_async, items):
     )
 
 
+def test_unique_with_async_gen(env_async):
+    items = ["a", "b", "c", "c", "a", "d", "z"]
+    tmpl = env_async.from_string("{{ items|reject('==', 'z')|unique|list }}")
+    out = tmpl.render(items=items)
+    assert out == "['a', 'b', 'c', 'd']"
+
+
 def test_custom_async_filter(env_async):
     async def customfilter(val):
         return str(val)