diff --git a/spectator-api/src/main/java/com/netflix/spectator/api/ArrayTagSet.java b/spectator-api/src/main/java/com/netflix/spectator/api/ArrayTagSet.java
index fed23b148..aaf7967c0 100644
--- a/spectator-api/src/main/java/com/netflix/spectator/api/ArrayTagSet.java
+++ b/spectator-api/src/main/java/com/netflix/spectator/api/ArrayTagSet.java
@@ -22,6 +22,7 @@
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 import java.util.concurrent.ConcurrentMap;
 import java.util.function.BiPredicate;
 import java.util.function.Predicate;
@@ -150,6 +151,11 @@ ArrayTagSet addAll(Iterable<Tag> ts) {
         checkForNullValues(newTags);
         return addAll(newTags, newTags.length);
       }
+    } else if (ts instanceof TagList) {
+      if (ts instanceof ArrayTagSet) {
+        return addAll((ArrayTagSet) ts);
+      }
+     return addAll((TagList) ts);
     } else {
       List<Tag> data = new ArrayList<>();
       for (Tag t : ts) {
@@ -210,6 +216,33 @@ private ArrayTagSet addAll(String[] ts, int tsLength) {
     }
   }
 
+  private ArrayTagSet addAll(ArrayTagSet ts) {
+    if (ts == this || ts.isEmpty()) {
+      return this;
+    }
+    if (isEmpty()) {
+      return ts;
+    }
+    String[] newTags = new String[length + ts.length];
+    int newLength = merge(newTags, tags, length, ts.tags, ts.length);
+    return new ArrayTagSet(newTags, newLength);
+  }
+
+  private ArrayTagSet addAll(TagList ts) {
+    int size = ts.size();
+
+    if (size == 0) {
+      return this;
+    }
+    String[] newTags = new String[size * 2];
+    int j = 0;
+    for (int i = 0; i < size; i++) {
+      newTags[j++] = Objects.requireNonNull(ts.getKey(i), "tag keys cannot be null");
+      newTags[j++] = Objects.requireNonNull(ts.getValue(i), "tag values cannot be null");
+    }
+    return addAll(newTags, newTags.length);
+  }
+
   /** Add a collection of tags to the set. */
   ArrayTagSet addAll(Tag[] ts) {
     return addAll(ts, ts.length);
diff --git a/spectator-api/src/test/java/com/netflix/spectator/api/ArrayTagSetTest.java b/spectator-api/src/test/java/com/netflix/spectator/api/ArrayTagSetTest.java
index 71c158660..36c2c8169 100644
--- a/spectator-api/src/test/java/com/netflix/spectator/api/ArrayTagSetTest.java
+++ b/spectator-api/src/test/java/com/netflix/spectator/api/ArrayTagSetTest.java
@@ -226,6 +226,27 @@ public void testMergeTag() {
     Assertions.assertEquals(expected, initial.addAll(update));
   }
 
+  @Test
+  public void testMergeWithSelf() {
+    ArrayTagSet tags = ArrayTagSet.create("k1", "v1");
+    ArrayTagSet updated = tags.addAll(tags);
+    Assertions.assertSame(tags, updated);
+  }
+
+  @Test
+  public void testMergeWithEmpty() {
+    ArrayTagSet tags = ArrayTagSet.create("k1", "v1");
+    ArrayTagSet updated = tags.addAll(ArrayTagSet.EMPTY);
+    Assertions.assertSame(tags, updated);
+  }
+
+  @Test
+  public void testEmptyMergeWithNonEmpty() {
+    ArrayTagSet tags = ArrayTagSet.create("k1", "v1");
+    ArrayTagSet updated = ArrayTagSet.EMPTY.addAll(tags);
+    Assertions.assertSame(tags, updated);
+  }
+
   @Test
   public void testMergeTagWithSameKey() {
     ArrayTagSet initial = ArrayTagSet.create("k1", "v1");
@@ -503,4 +524,53 @@ public void compareToDifferentSizes() {
     Assertions.assertEquals(-1, a.compareTo(b));
     Assertions.assertEquals(1, b.compareTo(a));
   }
+
+  @Test
+  public void mergeTagList() {
+    TagList tagList = new TagList() {
+      @Override
+      public String getKey(int i) {
+        return "k" + ++i;
+      }
+
+      @Override
+      public String getValue(int i) {
+        return "v" + ++i;
+      }
+
+      @Override
+      public int size() {
+        return 3;
+      }
+    };
+    ArrayTagSet tags = ArrayTagSet.create("k1", "v1", "k2", "v2");
+    ArrayTagSet updated = tags.addAll(tagList);
+    ArrayTagSet expected = ArrayTagSet.create("k1", "v1", "k2", "v2", "k3", "v3");
+    Assertions.assertEquals(expected, updated);
+  }
+
+  @Test
+  public void mergeEmptyTagList() {
+    TagList empty = new TagList() {
+      @Override
+      public String getKey(int i) {
+        throw new IndexOutOfBoundsException();
+      }
+
+      @Override
+      public String getValue(int i) {
+        throw new IndexOutOfBoundsException();
+      }
+
+      @Override
+      public int size() {
+        return 0;
+      }
+    };
+
+    ArrayTagSet tags = ArrayTagSet.create("k1", "v1", "k2", "v2");
+    ArrayTagSet updated = tags.addAll(empty);
+
+    Assertions.assertSame(tags, updated);
+  }
 }