powercoder23
diff --git a/‎__tests__/Set.ts
+8 b/‎__tests__/Set.ts
+8
diff --git a/‎dist/immutable.js
+2-2 b/‎dist/immutable.js
+2-2
@@ -198,6 +198,14 @@ describe('Set', () => {
     expect(Immutable.is(s1, v1)).toBe(false);
   });
 
+  it('can use union in a withMutation', () => {
+    var js = Immutable.Set().withMutations(set => {
+      set.union([ 'a' ]);
+      set.add('b');
+    }).toJS();
+    expect(js).toEqual(['a', 'b']);
+  });
+
   // TODO: more tests
 
 });
@@ -2456,7 +2456,7 @@
     if (iters.length === 0) {
       return collection;
     }
-    if (collection.size === 0 && iters.length === 1) {
+    if (collection.size === 0 && !collection.__ownerID && iters.length === 1) {
       return collection.constructor(iters[0]);
     }
     return collection.withMutations(function(collection ) {
@@ -3559,7 +3559,7 @@
       if (iters.length === 0) {
         return this;
       }
-      if (this.size === 0 && iters.length === 1) {
+      if (this.size === 0 && !this.__ownerID && iters.length === 1) {
         return this.constructor(iters[0]);
       }
       return this.withMutations(function(set ) {
Original file line number	Diff line number	Diff line change
`@@ -2456,7 +2456,7 @@`
`2456`	`2456`	`if (iters.length === 0) {`
`2457`	`2457`	`return collection;`
`2458`	`2458`	`}`
`2459`		`- if (collection.size === 0 && iters.length === 1) {`
	`2459`	`+ if (collection.size === 0 && !collection.__ownerID && iters.length === 1) {`
`2460`	`2460`	`return collection.constructor(iters[0]);`
`2461`	`2461`	`}`
`2462`	`2462`	`return collection.withMutations(function(collection ) {`
`@@ -3559,7 +3559,7 @@`
`3559`	`3559`	`if (iters.length === 0) {`
`3560`	`3560`	`return this;`
`3561`	`3561`	`}`
`3562`		`- if (this.size === 0 && iters.length === 1) {`
	`3562`	`+ if (this.size === 0 && !this.__ownerID && iters.length === 1) {`
`3563`	`3563`	`return this.constructor(iters[0]);`
`3564`	`3564`	`}`
`3565`	`3565`	`return this.withMutations(function(set ) {`