diff --git a/src/database.rs b/src/database.rs
index b46bb3c..b685743 100644
--- a/src/database.rs
+++ b/src/database.rs
@@ -26,10 +26,14 @@ use StateGroupEntry;
 
 /// Fetch the entries in state_groups_state (and their prev groups) for the
 /// given `room_id` by connecting to the postgres database at `db_url`.
-pub fn get_data_from_db(db_url: &str, room_id: &str) -> BTreeMap<i64, StateGroupEntry> {
+pub fn get_data_from_db(
+    db_url: &str,
+    room_id: &str,
+    max_state_group: Option<i64>,
+) -> BTreeMap<i64, StateGroupEntry> {
     let conn = Connection::connect(db_url, TlsMode::None).unwrap();
 
-    let mut state_group_map = get_initial_data_from_db(&conn, room_id);
+    let mut state_group_map = get_initial_data_from_db(&conn, room_id, max_state_group);
 
     println!("Got initial state from database. Checking for any missing state groups...");
 
@@ -69,21 +73,36 @@ pub fn get_data_from_db(db_url: &str, room_id: &str) -> BTreeMap<i64, StateGroup
 
 /// Fetch the entries in state_groups_state (and their prev groups) for the
 /// given `room_id` by fetching all state with the given `room_id`.
-fn get_initial_data_from_db(conn: &Connection, room_id: &str) -> BTreeMap<i64, StateGroupEntry> {
-    let stmt = conn
-        .prepare(
-            r#"
-                SELECT m.id, prev_state_group, type, state_key, s.event_id
-                FROM state_groups AS m
-                LEFT JOIN state_groups_state AS s ON (m.id = s.state_group)
-                LEFT JOIN state_group_edges AS e ON (m.id = e.state_group)
-                WHERE m.room_id = $1
-            "#,
-        )
-        .unwrap();
+fn get_initial_data_from_db(
+    conn: &Connection,
+    room_id: &str,
+    max_state_group: Option<i64>,
+) -> BTreeMap<i64, StateGroupEntry> {
+    let sql = format!(
+        r#"
+        SELECT m.id, prev_state_group, type, state_key, s.event_id
+        FROM state_groups AS m
+        LEFT JOIN state_groups_state AS s ON (m.id = s.state_group)
+        LEFT JOIN state_group_edges AS e ON (m.id = e.state_group)
+        WHERE m.room_id = $1 {}
+    "#,
+        if max_state_group.is_some() {
+            "AND state_group <= $2"
+        } else {
+            ""
+        }
+    );
+
+    let stmt = conn.prepare(&sql).unwrap();
 
     let trans = conn.transaction().unwrap();
-    let mut rows = stmt.lazy_query(&trans, &[&room_id], 1000).unwrap();
+
+    let mut rows = if let Some(s) = max_state_group {
+        stmt.lazy_query(&trans, &[&room_id, &s], 1000)
+    } else {
+        stmt.lazy_query(&trans, &[&room_id], 1000)
+    }
+    .unwrap();
 
     let mut state_group_map: BTreeMap<i64, StateGroupEntry> = BTreeMap::new();
 
diff --git a/src/main.rs b/src/main.rs
index 3c0eb5a..2bbdb22 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -124,6 +124,12 @@ fn main() {
                 .help("The room to process")
                 .takes_value(true)
                 .required(true),
+        ).arg(
+            Arg::with_name("max_state_group")
+                .short("s")
+                .help("The maximum state group to process up to")
+                .takes_value(true)
+                .required(false),
         ).arg(
             Arg::with_name("output_file")
                 .short("o")
@@ -161,17 +167,22 @@ fn main() {
     let mut output_file = matches
         .value_of("output_file")
         .map(|path| File::create(path).unwrap());
+
     let room_id = matches
         .value_of("room_id")
         .expect("room_id should be required since no file");
 
+    let max_state_group = matches
+        .value_of("max_state_group")
+        .map(|s| s.parse().expect("max_state_group must be an integer"));
+
     let transactions = matches.is_present("transactions");
 
     let level_sizes = value_t_or_exit!(matches, "level_sizes", LevelSizes);
 
     // First we need to get the current state groups
     println!("Fetching state from DB for room '{}'...", room_id);
-    let state_group_map = database::get_data_from_db(db_url, room_id);
+    let state_group_map = database::get_data_from_db(db_url, room_id, max_state_group);
 
     println!("Number of state groups: {}", state_group_map.len());