diff --git a/changelog.d/74.dev.md b/changelog.d/74.dev.md
new file mode 100644
index 0000000..1488035
--- /dev/null
+++ b/changelog.d/74.dev.md
@@ -0,0 +1 @@
+Improve details of internal error message<ISSUES_LIST>.
diff --git a/src/vector.rs b/src/vector.rs
index d86a7b0..d3e548b 100644
--- a/src/vector.rs
+++ b/src/vector.rs
@@ -38,9 +38,9 @@ fn swap_endian<'py>(
     let bytes = &data.as_bytes();
     let len = bytes.len();
     if len % type_size != 0 {
-        return Err(PyErr::new::<PyValueError, _>(
-            "Data length not a multiple of type_size",
-        ));
+        return Err(PyErr::new::<PyValueError, _>(format!(
+            "Data length {len} not a multiple of type_size {type_size}",
+        )));
     }
 
     PyBytes::new_with(py, bytes.len(), |out| {