diff --git a/tests/amount_precision.rs b/tests/amount_precision.rs
new file mode 100644
index 0000000..a295748
--- /dev/null
+++ b/tests/amount_precision.rs
@@ -0,0 +1,14 @@
+//! ISO 20022 allows an amount 18 significant digits. f64 carries 15.
+
+use mx_message::document::camt_053_001_08::ActiveOrHistoricCurrencyAndAmount;
+
+#[test]
+fn an_eighteen_digit_amount_is_not_rounded() {
+    let xml = r#"<Amt Ccy="KZT">123456789012345678</Amt>"#;
+    let amt: ActiveOrHistoricCurrencyAndAmount =
+        quick_xml::de::from_str(xml).expect("the amount parses");
+
+    // Nothing here is exotic: 18 digits is what the standard permits, and the
+    // nearest f64 to this one is 123456789012345680.
+    assert_eq!(amt.value.to_string(), "123456789012345678");
+}