diff --git a/Cargo.toml b/Cargo.toml
index 08dd734..eb560d5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -3,7 +3,7 @@ name = "orderbook"
 version = "0.2.0"
 authors = ["Łukasz Bednarski <lukasz@bednarski.me>"]
 edition = "2021"
-rust-version = "1.80.1"
+rust-version = "1.70"
 
 [dependencies]
 either = "1.13.0"
diff --git a/src/book.rs b/src/book.rs
index 68b6c65..d72925e 100644
--- a/src/book.rs
+++ b/src/book.rs
@@ -327,3 +327,19 @@ fn is_deeper(a: f64, b: f64, side: &Side) -> bool {
         Side::Ask => a + EPSILON < b,
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_empty_order_book() {
+        let ob = OrderBook::new();
+        assert!(ob.get_ladder(&Side::Bid).is_empty());
+        assert!(ob.get_ladder(&Side::Ask).is_empty());
+        assert_eq!(ob.best_bid(), None);
+        assert_eq!(ob.best_bid_size(), None);
+        assert_eq!(ob.best_ask(), None);
+        assert_eq!(ob.best_ask_size(), None);
+    }
+}