diff --git a/hadoop-hdfs-project/hadoop-hdfs-httpfs/src/main/java/org/apache/hadoop/lib/service/instrumentation/InstrumentationService.java b/hadoop-hdfs-project/hadoop-hdfs-httpfs/src/main/java/org/apache/hadoop/lib/service/instrumentation/InstrumentationService.java
index ee4455c9998df..0cd07db4be03b 100644
--- a/hadoop-hdfs-project/hadoop-hdfs-httpfs/src/main/java/org/apache/hadoop/lib/service/instrumentation/InstrumentationService.java
+++ b/hadoop-hdfs-project/hadoop-hdfs-httpfs/src/main/java/org/apache/hadoop/lib/service/instrumentation/InstrumentationService.java
@@ -226,6 +226,9 @@ long[] getValues() {
       lock.lock();
       try {
         long[] values = new long[4];
+        if (last < 0) {
+          return values;
+        }
         values[LAST_TOTAL] = total[last];
         values[LAST_OWN] = own[last];
         int limit = (full) ? size : (last + 1);
diff --git a/hadoop-hdfs-project/hadoop-hdfs-httpfs/src/test/java/org/apache/hadoop/lib/service/instrumentation/TestInstrumentationService.java b/hadoop-hdfs-project/hadoop-hdfs-httpfs/src/test/java/org/apache/hadoop/lib/service/instrumentation/TestInstrumentationService.java
index 86d42ccdf2d79..6a7e1e731fe0e 100644
--- a/hadoop-hdfs-project/hadoop-hdfs-httpfs/src/test/java/org/apache/hadoop/lib/service/instrumentation/TestInstrumentationService.java
+++ b/hadoop-hdfs-project/hadoop-hdfs-httpfs/src/test/java/org/apache/hadoop/lib/service/instrumentation/TestInstrumentationService.java
@@ -232,6 +232,24 @@ public void timer() throws Exception {
     assertEquals(json.get("avgOwn"), values[InstrumentationService.Timer.AVG_OWN]);
   }
 
+  @Test
+  public void timerGetValuesBeforeAnyCron() throws Exception {
+    // HDFS-16029: getValues() on a fresh Timer (last == -1) must not throw
+    // ArrayIndexOutOfBoundsException or divide-by-zero; it should return zeros.
+    InstrumentationService.Timer timer = new InstrumentationService.Timer(2);
+    long[] values = timer.getValues();
+    assertEquals(4, values.length);
+    assertEquals(0, values[InstrumentationService.Timer.LAST_TOTAL]);
+    assertEquals(0, values[InstrumentationService.Timer.LAST_OWN]);
+    assertEquals(0, values[InstrumentationService.Timer.AVG_TOTAL]);
+    assertEquals(0, values[InstrumentationService.Timer.AVG_OWN]);
+
+    // toJSONString() also calls getValues() via getJSON() — must not throw either
+    String json = timer.toJSONString();
+    assertNotNull(json);
+    assertTrue(json.contains("lastTotal"));
+  }
+
   @Test
   public void sampler() throws Exception {
     final long value[] = new long[1];