diff --git a/TODO.md b/TODO.md
index 6385244..cc5f8f3 100644
--- a/TODO.md
+++ b/TODO.md
@@ -20,6 +20,10 @@ regress.
 
 # Completed Steps
 
+- 2026-10-01: Two database writes at the same moment no longer fail with
+  "database is locked": each transaction now takes the write lock when it begins
+  and waits up to 5 seconds for another writer to finish (#253).
+
 - 2026-10-01: Builds attach a BuildKit session, as the docker command line does,
   so a base image that is not on the host is pulled instead of the build failing
   with "no active sessions" on Docker Engine 27. Container logs, and so the
diff --git a/internal/database/database.go b/internal/database/database.go
index 929ef5e..75cc220 100644
--- a/internal/database/database.go
+++ b/internal/database/database.go
@@ -137,8 +137,11 @@ func (d *Database) connect(ctx context.Context) error {
 		return fmt.Errorf("failed to create data directory: %w", err)
 	}
 
-	// Open database with WAL mode and foreign keys
-	dsn := dbPath + "?_journal_mode=WAL&_foreign_keys=on"
+	// Open database with WAL mode and foreign keys. Transactions take the
+	// write lock when they begin and wait up to 5s for another writer,
+	// instead of failing with "database is locked" when both write.
+	dsn := dbPath + "?_journal_mode=WAL&_foreign_keys=on" +
+		"&_txlock=immediate&_busy_timeout=5000"
 
 	database, err := sql.Open("sqlite3", dsn)
 	if err != nil {