diff --git a/src/main/java/ch/naviqore/gtfs/schedule/GtfsScheduleFile.java b/src/main/java/ch/naviqore/gtfs/schedule/GtfsScheduleFile.java
index 8c924b59..f4f442ed 100644
--- a/src/main/java/ch/naviqore/gtfs/schedule/GtfsScheduleFile.java
+++ b/src/main/java/ch/naviqore/gtfs/schedule/GtfsScheduleFile.java
@@ -9,17 +9,25 @@
 @RequiredArgsConstructor
 @Getter
 public enum GtfsScheduleFile {
-    AGENCY("agency.txt"),
-    CALENDAR("calendar.txt"),
-    CALENDAR_DATES("calendar_dates.txt"),
-    // FARE_ATTRIBUTES("fare_attributes.txt"),
-    // FARE_RULES("fare_rules.txt"),
-    // FREQUENCIES("frequencies.txt"),
-    STOPS("stops.txt"),
-    ROUTES("routes.txt"),
-    // SHAPES("shapes.txt"),
-    TRIPS("trips.txt"),
-    STOP_TIMES("stop_times.txt");
+    // FEED_INFO("feed_info.txt", Presence.OPTIONAL),
+    // ATTRIBUTIONS("attributions.txt", Presence.OPTIONAL),
+    AGENCY("agency.txt", Presence.REQUIRED),
+    CALENDAR("calendar.txt", Presence.CONDITIONALLY_REQUIRED),
+    CALENDAR_DATES("calendar_dates.txt", Presence.CONDITIONALLY_REQUIRED),
+    // FARE_ATTRIBUTES("fare_attributes.txt", Presence.OPTIONAL),
+    // FARE_RULES("fare_rules.txt", Presence.OPTIONAL),
+    // FREQUENCIES("frequencies.txt", Presence.OPTIONAL),
+    STOPS("stops.txt", Presence.REQUIRED),
+    ROUTES("routes.txt", Presence.REQUIRED),
+    // SHAPES("shapes.txt", Presence.OPTIONAL),
+    TRIPS("trips.txt", Presence.REQUIRED),
+    STOP_TIMES("stop_times.txt", Presence.REQUIRED);
+    // TRANSFERS("transfers.txt", Presence.OPTIONAL);
 
     private final String fileName;
+    private final Presence presence;
+
+    public enum Presence {
+        REQUIRED, OPTIONAL, CONDITIONALLY_REQUIRED, CONDITIONALLY_FORBIDDEN, RECOMMENDED
+    }
 }
diff --git a/src/main/java/ch/naviqore/gtfs/schedule/GtfsScheduleReader.java b/src/main/java/ch/naviqore/gtfs/schedule/GtfsScheduleReader.java
index 86ce17b6..9f364bd0 100644
--- a/src/main/java/ch/naviqore/gtfs/schedule/GtfsScheduleReader.java
+++ b/src/main/java/ch/naviqore/gtfs/schedule/GtfsScheduleReader.java
@@ -12,6 +12,7 @@
 
 import java.io.File;
 import java.io.FileInputStream;
+import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.nio.charset.StandardCharsets;
@@ -44,8 +45,8 @@ private static void readFromDirectory(File directory, GtfsScheduleParser parser)
             if (csvFile.exists()) {
                 log.info("Reading GTFS CSV file: {}", csvFile.getAbsolutePath());
                 readCsvFile(csvFile, parser, fileType);
-            } else {
-                log.warn("GTFS CSV file {} not found", csvFile.getAbsolutePath());
+            } else if (fileType.getPresence() == GtfsScheduleFile.Presence.REQUIRED) {
+                throw new FileNotFoundException("Required GTFS CSV file" + csvFile.getAbsolutePath() + " not found");
             }
         }
     }
@@ -63,8 +64,8 @@ private static void readFromZip(File zipFile, GtfsScheduleParser parser) throws
                             .get(), StandardCharsets.UTF_8)) {
                         readCsvRecords(reader, parser, fileType);
                     }
-                } else {
-                    log.warn("GTFS file {} not found in ZIP", fileType.getFileName());
+                } else if (fileType.getPresence() == GtfsScheduleFile.Presence.REQUIRED) {
+                    throw new FileNotFoundException("Required GTFS CSV file" + fileType.getFileName() + " not found in ZIP");
                 }
             }
         }