diff --git a/src/dc_tools.rs b/src/dc_tools.rs
index 8f829aee1..40f78c75e 100644
--- a/src/dc_tools.rs
+++ b/src/dc_tools.rs
@@ -803,8 +803,19 @@ pub unsafe fn dc_create_outgoing_rfc724_mid(
     ret
 }
 
-/// Extract our group ID from Message-IDs as `Gr.12345678901.morerandom@domain.de`
-/// `12345678901` is the wanted ID in this example.
+/// Extract the group id (grpid) from a message id (mid)
+///
+/// # Arguments
+///
+/// * `mid` - A string that holds the message id
+///
+/// # Examples
+///
+/// ```
+/// let mid = "Gr.12345678901.morerandom@domain.de";
+/// let grpid = dc_extract_grpid_from_rfc724_mid(mid);
+/// assert_eq!(grpid, Some("12345678901"));
+/// ```
 pub fn dc_extract_grpid_from_rfc724_mid(mid: &str) -> Option<&str> {
     if mid.len() < 9 || !mid.starts_with("Gr.") {
         return None;