diff --git a/src/hello.rs b/src/hello.rs
index 37229ec5b..1c1c14348 100644
--- a/src/hello.rs
+++ b/src/hello.rs
@@ -179,9 +179,27 @@ pub(crate) struct HelloCommandResponse {
 
     /// The server-generated ID for the connection the "hello" command was run on.
     /// Present on server versions 4.2+.
+    #[serde(deserialize_with = "deserialize_connection_id", default)]
     pub connection_id: Option<i64>,
 }
 
+fn deserialize_connection_id<'de, D: serde::Deserializer<'de>>(
+    de: D,
+) -> std::result::Result<Option<i64>, D::Error> {
+    #[derive(Deserialize)]
+    #[serde(untagged)]
+    enum Helper {
+        Int32(i32),
+        Int64(i64),
+        Double(f64),
+    }
+    Ok(Some(match Helper::deserialize(de)? {
+        Helper::Int32(v) => v as i64,
+        Helper::Int64(v) => v,
+        Helper::Double(v) => v as i64,
+    }))
+}
+
 impl HelloCommandResponse {
     pub(crate) fn server_type(&self) -> ServerType {
         if self.msg.as_deref() == Some("isdbgrid") {
diff --git a/src/test.rs b/src/test.rs
index 378ddea6e..dec6e3388 100644
--- a/src/test.rs
+++ b/src/test.rs
@@ -12,6 +12,7 @@ mod cursor;
 mod db;
 #[cfg(all(not(feature = "sync"), not(feature = "tokio-sync")))]
 mod documentation_examples;
+mod hello;
 mod index_management;
 #[cfg(all(not(feature = "sync"), not(feature = "tokio-sync")))]
 mod lambda_examples;
diff --git a/src/test/hello.rs b/src/test/hello.rs
new file mode 100644
index 000000000..2b21c6562
--- /dev/null
+++ b/src/test/hello.rs
@@ -0,0 +1,37 @@
+use bson::{doc, Bson};
+
+use crate::hello::HelloCommandResponse;
+
+#[test]
+fn parse_connection_id() {
+    let mut parsed: HelloCommandResponse = bson::from_document(doc! {
+        "connectionId": Bson::Int32(42),
+        "maxBsonObjectSize": 0,
+        "maxMessageSizeBytes": 0,
+    })
+    .unwrap();
+    assert_eq!(parsed.connection_id, Some(42));
+
+    parsed = bson::from_document(doc! {
+        "connectionId": Bson::Int64(13),
+        "maxBsonObjectSize": 0,
+        "maxMessageSizeBytes": 0,
+    })
+    .unwrap();
+    assert_eq!(parsed.connection_id, Some(13));
+
+    parsed = bson::from_document(doc! {
+        "connectionId": Bson::Double(1066.0),
+        "maxBsonObjectSize": 0,
+        "maxMessageSizeBytes": 0,
+    })
+    .unwrap();
+    assert_eq!(parsed.connection_id, Some(1066));
+
+    parsed = bson::from_document(doc! {
+        "maxBsonObjectSize": 0,
+        "maxMessageSizeBytes": 0,
+    })
+    .unwrap();
+    assert_eq!(parsed.connection_id, None);
+}