diff --git a/inginious/common/tasks_problems.py b/inginious/common/tasks_problems.py
index ca0ae88a8..77bb0360d 100644
--- a/inginious/common/tasks_problems.py
+++ b/inginious/common/tasks_problems.py
@@ -236,7 +236,7 @@ def parse_problem(self, problem_content):
             if problem_content["allowed_exts"] == "":
                 del problem_content["allowed_exts"]
             else:
-                problem_content["allowed_exts"] = problem_content["allowed_exts"].split(',')
+                problem_content["allowed_exts"] = [extension.strip() for extension in problem_content["allowed_exts"].split(',')]
 
         if "max_size" in problem_content:
             try: