diff --git a/psb2/psb2.py b/psb2/psb2.py
index 937c1be..4b6c849 100644
--- a/psb2/psb2.py
+++ b/psb2/psb2.py
@@ -101,9 +101,13 @@ def fetch_examples(datasets_directory, problem_name, n_train, n_test, format='ps
     assert n_train < 1000000, "Cannot sample more than 1 million examples"
     assert n_test < 1000000, "Cannot sample more than 1 million examples"
 
+    # Check whether problem_name is a valid PSB2 problem
+    if problem_name.strip() not in get_problem_names():
+        raise AttributeError('The provided problem_name (' + problem_name.strip() +') is not available in the list of PSB2 problems, which are the followings: ' + ', '.join(get_problem_names()) + '.')
+
     # Load data
-    edge_data = fetch_and_possibly_cache_data(datasets_directory, problem_name, "edge")
-    random_data = fetch_and_possibly_cache_data(datasets_directory, problem_name, "random")
+    edge_data = fetch_and_possibly_cache_data(datasets_directory, problem_name.strip(), "edge")
+    random_data = fetch_and_possibly_cache_data(datasets_directory, problem_name.strip(), "random")
 
     # Seed RNG source
     random.seed(seed)
@@ -124,4 +128,4 @@ def fetch_examples(datasets_directory, problem_name, n_train, n_test, format='ps
 
 def get_problem_names():
     """Returns a list of strings of the problem names in PSB2."""
-    return PROBLEMS
+    return [pro for pro in PROBLEMS]