diff --git a/src/octoprint/util/__init__.py b/src/octoprint/util/__init__.py
index ea4012a3..cb47af81 100644
--- a/src/octoprint/util/__init__.py
+++ b/src/octoprint/util/__init__.py
@@ -306,6 +306,11 @@ def find_collision_free_name(filename, extension, existing_filenames, max_power=
 
 	# TODO unit test!
 
+	if not isinstance(filename, unicode):
+		filename = unicode(filename)
+	if not isinstance(extension, unicode):
+		extension = unicode(extension)
+
 	def make_valid(text):
 		return re.sub(r"\s+", "_", text.translate({ord(i):None for i in ".\"/\\[]:;=,"})).lower()
 
diff --git a/src/octoprint/util/virtual.py b/src/octoprint/util/virtual.py
index 32e32cdb..633aa301 100644
--- a/src/octoprint/util/virtual.py
+++ b/src/octoprint/util/virtual.py
@@ -313,7 +313,7 @@ class VirtualPrinter():
 	def _selectSdFile(self, filename):
 		if filename.startswith("/"):
 			filename = filename[1:]
-		file = os.path.join(self._virtualSd, filename).lower()
+		file = os.path.join(self._virtualSd, filename.lower())
 		if not os.path.exists(file) or not os.path.isfile(file):
 			self.outgoing.put("open failed, File: %s." % filename)
 		else: