diff --git a/src/main/java/com/zaxxer/hikari/util/DriverDataSource.java b/src/main/java/com/zaxxer/hikari/util/DriverDataSource.java
index 231b062c2..de78101fa 100644
--- a/src/main/java/com/zaxxer/hikari/util/DriverDataSource.java
+++ b/src/main/java/com/zaxxer/hikari/util/DriverDataSource.java
@@ -125,7 +125,9 @@ public Connection getConnection(final String username, final String password) th
       final Properties cloned = (Properties) driverProperties.clone();
       if (username != null) {
          cloned.put("user", username);
-         cloned.put("username", username);
+         if (cloned.containsKey("username")) {
+            cloned.put("username", username);
+         }
       }
       if (password != null) {
          cloned.put("password", password);