diff --git a/src/main/java/com/zaxxer/hikari/HikariConfig.java b/src/main/java/com/zaxxer/hikari/HikariConfig.java
index e2b34dc7d..6f6c3879a 100644
--- a/src/main/java/com/zaxxer/hikari/HikariConfig.java
+++ b/src/main/java/com/zaxxer/hikari/HikariConfig.java
@@ -194,14 +194,14 @@ else if (connectionTimeoutMs < SOFT_TIMEOUT_FLOOR) {
 
    /** {@inheritDoc} */
    @Override
-   public long getIdleTimeout()
+   public synchronized long getIdleTimeout()
    {
       return idleTimeout;
    }
 
    /** {@inheritDoc} */
    @Override
-   public void setIdleTimeout(long idleTimeoutMs)
+   public synchronized void setIdleTimeout(long idleTimeoutMs)
    {
       if (idleTimeoutMs < 0) {
          throw new IllegalArgumentException("idleTimeout cannot be negative");
diff --git a/src/test/java/com/zaxxer/hikari/db/BasicPoolTest.java b/src/test/java/com/zaxxer/hikari/db/BasicPoolTest.java
index 07c530b99..ececa0fe0 100644
--- a/src/test/java/com/zaxxer/hikari/db/BasicPoolTest.java
+++ b/src/test/java/com/zaxxer/hikari/db/BasicPoolTest.java
@@ -77,14 +77,14 @@ public void testIdleTimeout() throws InterruptedException, SQLException
       System.setProperty("com.zaxxer.hikari.housekeeping.periodMs", "1000");
 
       try (HikariDataSource ds = new HikariDataSource(config)) {
+         getUnsealedConfig(ds).setIdleTimeout(3000);
+
          System.clearProperty("com.zaxxer.hikari.housekeeping.periodMs");
 
          SECONDS.sleep(1);
 
          HikariPool pool = getPool(ds);
 
-         getUnsealedConfig(ds).setIdleTimeout(3000);
-
          assertEquals("Total connections not as expected", 5, pool.getTotalConnections());
          assertEquals("Idle connections not as expected", 5, pool.getIdleConnections());