diff --git a/mnemosyne/library/api/serializers.py b/mnemosyne/library/api/serializers.py
index 22eea70..c4cb03c 100644
--- a/mnemosyne/library/api/serializers.py
+++ b/mnemosyne/library/api/serializers.py
@@ -211,7 +211,7 @@ class IngestRequestSerializer(serializers.Serializer):
     file_type = serializers.CharField(required=False, allow_blank=True, default="")
     file_size = serializers.IntegerField(required=False, default=0)
     content_hash = serializers.CharField(max_length=64)
-    source = serializers.CharField(required=False, allow_blank=True, default="")
+    source = serializers.CharField(required=False, allow_blank=True, default="", max_length=50)
     source_ref = serializers.CharField(required=False, allow_blank=True, default="")
 
     def validate(self, data):