diff --git a/CHANGELOG.md b/CHANGELOG.md
index 85fc7d31..575f1f5c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -482,3 +482,4 @@ The old `smart_open.smart_open` function is deprecated, but continues to work as
 
   - support for multistream bzip files (PR #9, @pombredanne)
   - introduce this CHANGELOG
+
diff --git a/smart_open/s3.py b/smart_open/s3.py
index 09433ad7..60ae2a99 100644
--- a/smart_open/s3.py
+++ b/smart_open/s3.py
@@ -1209,8 +1209,8 @@ def write(self, b):
         return length
 
     def terminate(self):
-        """Nothing to cancel in single-part uploads."""
-        return
+        self._buf = None
+        logger.debug('%s: terminated singlepart upload', self)
 
     #
     # Internal methods.
diff --git a/smart_open/tests/test_s3.py b/smart_open/tests/test_s3.py
index ff44ad4f..61aec986 100644
--- a/smart_open/tests/test_s3.py
+++ b/smart_open/tests/test_s3.py
@@ -795,6 +795,26 @@ def test_str(self):
         with smart_open.s3.open(BUCKET_NAME, 'key', 'wb', multipart_upload=False) as fout:
             assert str(fout) == "smart_open.s3.SinglepartWriter('test-smartopen', 'key')"
 
+    def test_ensure_no_side_effects_on_exception(self):
+        class WriteError(Exception):
+            pass
+
+        s3_resource = _resource("s3")
+        obj = s3_resource.Object(BUCKET_NAME, KEY_NAME)
+
+        # wrap in closure to ease writer dereferencing
+        def _run():
+            with smart_open.s3.open(BUCKET_NAME, obj.key, "wb", multipart_upload=False) as fout:
+                fout.write(b"this should not be written")
+                raise WriteError
+
+        try:
+            _run()
+        except WriteError:
+            pass
+        finally:
+            self.assertRaises(s3_resource.meta.client.exceptions.NoSuchKey, obj.get)
+
 
 ARBITRARY_CLIENT_ERROR = botocore.client.ClientError(error_response={}, operation_name='bar')