diff --git a/src/Log4Mongo/MongoDBAppender.cs b/src/Log4Mongo/MongoDBAppender.cs
index 34947b1..44da558 100644
--- a/src/Log4Mongo/MongoDBAppender.cs
+++ b/src/Log4Mongo/MongoDBAppender.cs
@@ -159,10 +159,14 @@ private void SetCappedCollectionOptions(CreateCollectionOptions options)
 			var newCollectionMaxSize = unitResolver.Resolve(NewCollectionMaxSize);
 			var newCollectionMaxDocs = unitResolver.Resolve(NewCollectionMaxDocs);
 
-			if (newCollectionMaxSize > 0)
+			if ((newCollectionMaxSize > 0) || (newCollectionMaxDocs > 0))
 			{
 				options.Capped = true;
-				options.MaxSize = newCollectionMaxSize;
+
+				if (newCollectionMaxSize > 0)
+				{
+					options.MaxSize = newCollectionMaxSize;
+				}
 
 				if (newCollectionMaxDocs > 0)
 				{
@@ -269,4 +273,4 @@ private void CreateExpiryAfterIndex(IMongoCollection<BsonDocument> collection)
 				});
 		}
 	}
-}
\ No newline at end of file
+}