diff --git a/spec/std/array_spec.cr b/spec/std/array_spec.cr
index 0f44cfb6774e..51ed3e17d74b 100644
--- a/spec/std/array_spec.cr
+++ b/spec/std/array_spec.cr
@@ -117,6 +117,10 @@ describe "Array" do
       b = [4, 5, 6] * 10
       (a | b).should eq([1, 2, 3, 4, 5, 6])
     end
+
+    it "different types" do
+      ([1, 2, 3] | ["hello"]).should eq([1, 2, 3, "hello"])
+    end
   end
 
   it "does +" do
diff --git a/src/array.cr b/src/array.cr
index 30425c6869e3..1732fc8ddc6f 100644
--- a/src/array.cr
+++ b/src/array.cr
@@ -307,7 +307,7 @@ class Array(T)
     end
 
     Array(T | U).build(size + other.size) do |buffer|
-      set = Set(T).new
+      set = Set(T | U).new
       appender = buffer.appender
       each do |obj|
         appender << obj if set.add?(obj)