Index: core/kernel/db/db_connection.php
===================================================================
--- core/kernel/db/db_connection.php
+++ core/kernel/db/db_connection.php
@@ -393,7 +393,19 @@
 		 */
 		protected function callErrorHandler($sql)
 		{
-			return call_user_func($this->errorHandler, $this->errorCode, $this->errorMessage, $sql);
+			$error_msg = $this->errorMessage;
+
+			// Specify slave servers or nothing for master/single database setups.
+			if ( $this->serverIndex ) {
+				$error_msg .= ' [Server #' . $this->serverIndex . ']';
+			}
+
+			return call_user_func(
+				$this->errorHandler,
+				$this->errorCode,
+				$error_msg,
+				$sql
+			);
 		}
 
 		/**