diff --git a/smart_open/s3.py b/smart_open/s3.py
index c5959bdb..946f97ba 100644
--- a/smart_open/s3.py
+++ b/smart_open/s3.py
@@ -1189,18 +1189,31 @@ def iter_bucket(
 
     with smart_open.concurrency.create_pool(processes=workers) as pool:
         result_iterator = pool.imap_unordered(download_key, key_iterator)
-        for key_no, (key, content) in enumerate(result_iterator):
-            if True or key_no % 1000 == 0:
-                logger.info(
-                    "yielding key #%i: %s, size %i (total %.1fMB)",
-                    key_no, key, len(content), total_size / 1024.0 ** 2
-                )
-            yield key, content
-            total_size += len(content)
-
-            if key_limit is not None and key_no + 1 >= key_limit:
-                # we were asked to output only a limited number of keys => we're done
+        key_no = 0
+        while True:
+            try:
+                (key, content) = result_iterator.__next__()
+                if True or key_no % 1000 == 0:
+                    logger.info(
+                        "yielding key #%i: %s, size %i (total %.1fMB)",
+                        key_no, key, len(content), total_size / 1024.0 ** 2
+                    )
+                yield key, content
+                total_size += len(content)
+                if key_limit is not None and key_no + 1 >= key_limit:
+                    # we were asked to output only a limited number of keys => we're done
+                    break
+            except botocore.exceptions.ClientError as err:
+                if 'Error' in err.response and err.response['Error'].get('Code') == '404':
+                    logger.warning(
+                        "Encountered '404 Not Found' error for key #%i",
+                        key_no
+                    )
+                else:
+                    raise err
+            except StopIteration:
                 break
+            key_no += 1
     logger.info("processed %i keys, total size %i" % (key_no + 1, total_size))
 
 
diff --git a/smart_open/tests/test_s3.py b/smart_open/tests/test_s3.py
index 4e5ca5b1..09db09d2 100644
--- a/smart_open/tests/test_s3.py
+++ b/smart_open/tests/test_s3.py
@@ -1,10 +1,3 @@
-# -*- coding: utf-8 -*-
-#
-# Copyright (C) 2019 Radim Rehurek <me@radimrehurek.com>
-#
-# This code is distributed under the terms and conditions
-# from the MIT License (MIT).
-#
 from collections import defaultdict
 import functools
 import gzip
@@ -404,7 +397,6 @@ def test_read_empty_file(self):
 class MultipartWriterTest(unittest.TestCase):
     """
     Test writing into s3 files.
-
     """
     def setUp(self):
         ignore_resource_warnings()
@@ -559,7 +551,6 @@ def test_writebuffer(self):
 class SinglepartWriterTest(unittest.TestCase):
     """
     Test writing into s3 files using single part upload.
-
     """
     def setUp(self):
         ignore_resource_warnings()
@@ -681,6 +672,28 @@ def test_iter_bucket(self):
         results = list(smart_open.s3.iter_bucket(BUCKET_NAME))
         self.assertEqual(len(results), 10)
 
+    def test_iter_bucket_404(self):
+        populate_bucket()
+
+        def throw_404_error_for_key_4(*args):
+            if args[1] == "key_4":
+                raise botocore.exceptions.ClientError(
+                    error_response={"Error": {"Code": "404", "Message": "Not Found"}},
+                    operation_name="HeadObject",
+                )
+            else:
+                return [0]
+
+        with mock.patch("smart_open.s3._download_fileobj", side_effect=throw_404_error_for_key_4):
+            results = list(smart_open.s3.iter_bucket(BUCKET_NAME))
+            self.assertEqual(len(results), 9)
+
+    def test_iter_bucket_non_404(self):
+        populate_bucket()
+        with mock.patch("smart_open.s3._download_fileobj", side_effect=ARBITRARY_CLIENT_ERROR):
+            with pytest.raises(botocore.exceptions.ClientError):
+                list(smart_open.s3.iter_bucket(BUCKET_NAME))
+
     def test_deprecated_top_level_s3_iter_bucket(self):
         populate_bucket()
         with self.assertLogs(smart_open.logger.name, level='WARN') as cm: