diff --git a/lib/http/headers.rb b/lib/http/headers.rb
index fce7027f..0d6291dd 100644
--- a/lib/http/headers.rb
+++ b/lib/http/headers.rb
@@ -75,6 +75,14 @@ def [](name)
       end
     end
 
+    # Tells whenever header with given `name` is set or not.
+    #
+    # @return [Boolean]
+    def include?(name)
+      name = normalize_header name.to_s
+      @pile.any? { |k, _| k == name }
+    end
+
     # Returns Rack-compatible headers Hash
     #
     # @return [Hash]
diff --git a/spec/lib/http/headers_spec.rb b/spec/lib/http/headers_spec.rb
index ab6fccd7..863e0316 100644
--- a/spec/lib/http/headers_spec.rb
+++ b/spec/lib/http/headers_spec.rb
@@ -185,6 +185,26 @@
     end
   end
 
+  describe "#include?" do
+    before do
+      headers.add :content_type, "application/json"
+      headers.add :set_cookie,   "hoo=ray"
+      headers.add :set_cookie,   "woo=hoo"
+    end
+
+    it "tells whenever given headers is set or not" do
+      expect(headers.include?("Content-Type")).to be true
+      expect(headers.include?("Set-Cookie")).to be true
+      expect(headers.include?("Accept")).to be false
+    end
+
+    it "normalizes given header name" do
+      expect(headers.include?(:content_type)).to be true
+      expect(headers.include?(:set_cookie)).to be true
+      expect(headers.include?(:accept)).to be false
+    end
+  end
+
   describe "#to_h" do
     before do
       headers.add :content_type, "application/json"