diff --git a/config.py.example b/config.py.example
index 094d1f0..8ed8e28 100644
--- a/config.py.example
+++ b/config.py.example
@@ -18,16 +18,19 @@ def mp3_sources(data_dir, pattern, kbits):
         length = timedelta(minutes=size / (1000*kbits/8) / 60)
         return length
 
-    # Get a sorted list of all source files with start time and length
-    sources = []
-    for fn in os.listdir(data_dir):
-        try:
-            start_time = start_time_for_source_fn(fn)
-            length = length_for_source_fn(fn)
-            sources.append({'fn': os.path.join(data_dir, fn), 'start_time': start_time, 'length': length})
-        except ValueError:
-            pass
-    return sources
+    def get_sources():
+        # Get a sorted list of all source files with start time and length
+        sources = []
+        for fn in os.listdir(data_dir):
+            try:
+                start_time = start_time_for_source_fn(fn)
+                length = length_for_source_fn(fn)
+                sources.append({'fn': os.path.join(data_dir, fn), 'start_time': start_time, 'length': length})
+            except ValueError:
+                pass
+        return sources
+
+    return get_sources
 
 
 class Config:
@@ -43,7 +46,7 @@ class Config:
 
     # Here's the interesting part: configuring the source.
     #
-    # We need to return a list of dicts of source files with metadata, e.g.
+    # We need to return a function that returns a list of dicts of source files with metadata, e.g.
     # [ {"fn": "/path/to/foo-20:01.mp3", "start_time": datetime(...), "length": timedelta(hours=1)} ]
 
     data_dir   = os.environ.get('DATA_DIR') or '/var/tmp/prolefeeder-test-data'
diff --git a/prolefeeder.py b/prolefeeder.py
index 2167c49..d2352c5 100644
--- a/prolefeeder.py
+++ b/prolefeeder.py
@@ -87,8 +87,7 @@ def prepare_download(form):
     """Prepare a download given the user's request form"""
 
     # Get a sorted list of all source files with start time and length
-    sources = sorted(Config.SOURCES, key=lambda s: s['start_time'])
-    print(sources)
+    sources = sorted(Config.SOURCES(), key=lambda s: s['start_time'])
 
     # Only interested in the source files from the start file
     start_index = None