diff --git a/clearml/backend_interface/metrics/events.py b/clearml/backend_interface/metrics/events.py
index eac07b01..d1bedce8 100644
--- a/clearml/backend_interface/metrics/events.py
+++ b/clearml/backend_interface/metrics/events.py
@@ -229,7 +229,7 @@ class UploadEvent(MetricsEventAdapter):
         self._key = None
         self._count = self._get_metric_count(metric, variant)
         if not file_history_size:
-            file_history_size = self._file_history_size
+            file_history_size = int(self._file_history_size)
         self._filename = kwargs.pop('override_filename', None)
         if not self._filename:
             if file_history_size < 1:
@@ -248,7 +248,7 @@ class UploadEvent(MetricsEventAdapter):
         # e.g.: image.png -> .png or image.raw.gz -> .raw.gz
         filename_ext = kwargs.pop('override_filename_ext', None)
         if filename_ext is None:
-            filename_ext = self._format.lower() if self._image_data is not None else \
+            filename_ext = str(self._format).lower() if self._image_data is not None else \
                 '.' + '.'.join(pathlib2.Path(self._local_image_path).parts[-1].split('.')[1:])
         # always add file extension to the uploaded target file
         if filename_ext and filename_ext[0] != '.':
@@ -290,7 +290,7 @@ class UploadEvent(MetricsEventAdapter):
         local_file = None
         # don't provide file in case this event is out of the history window
         last_count = self._get_metric_count(self.metric, self.variant, next=False)
-        if abs(self._count - last_count) > self._file_history_size:
+        if abs(self._count - last_count) > int(self._file_history_size):
             output = None
         elif isinstance(self._image_data, (six.StringIO, six.BytesIO)):
             output = self._image_data
@@ -313,8 +313,8 @@ class UploadEvent(MetricsEventAdapter):
             # serialize image
             image = Image.fromarray(image_data)
             output = six.BytesIO()
-            image_format = Image.registered_extensions().get(self._format.lower(), 'JPEG')
-            image.save(output, format=image_format, quality=self._quality)
+            image_format = Image.registered_extensions().get(str(self._format).lower(), 'JPEG')
+            image.save(output, format=image_format, quality=int(self._quality))
             output.seek(0)
         else:
             # noinspection PyBroadException