diff --git a/app/db.py b/app/db.py
index 8798f9f..a0de3a8 100644
--- a/app/db.py
+++ b/app/db.py
@@ -20,6 +20,19 @@ _pool_lock = threading.Lock()
 
 
 def _build_pool() -> "pooling.MySQLConnectionPool":
+    # pool_size default of 24 covers transfer-bot at full tilt:
+    # CM_TRANSFER_MAX_THREADS defaults to 20, each thread can hold one
+    # connection for the duration of a transfer step. A smaller pool
+    # would surface as PoolError (caught silently by query/execute) and
+    # transfers would fail without obvious cause. mysql.connector caps
+    # pool_size at 32; if you bump CM_TRANSFER_MAX_THREADS, set
+    # DB_POOL_SIZE to at least the same value, capped at 32.
+    pool_size = int(os.getenv("DB_POOL_SIZE", "24"))
+    if pool_size > 32:
+        # Hard cap from mysql.connector; clamp here so the misconfigured
+        # value gets a clean message instead of a cryptic library error.
+        print(f"DB_POOL_SIZE={pool_size} exceeds mysql.connector max (32); clamping to 32")
+        pool_size = 32
     config = {
         "host": _get_required_env("DB_HOST"),
         "user": _get_required_env("DB_USER"),
@@ -28,7 +41,7 @@ def _build_pool() -> "pooling.MySQLConnectionPool":
         "port": int(_get_required_env("DB_PORT")),
         "connection_timeout": int(_get_required_env("DB_CONNECTION_TIMEOUT")),
         "pool_name": "cm_pool",
-        "pool_size": int(os.getenv("DB_POOL_SIZE", "8")),
+        "pool_size": pool_size,
         "pool_reset_session": True,
     }
     return pooling.MySQLConnectionPool(**config)