diff --git a/History.md b/History.md
index 10b15b2b6a..cbf13eb837 100644
--- a/History.md
+++ b/History.md
@@ -1,6 +1,7 @@
 unreleased
 ==========
 
+  * Fix error when `res.set` cannot add charset to `Content-Type`
   * deps: debug@2.6.3
     - Fix: `DEBUG_MAX_ARRAY_LENGTH`
   * deps: finalhandler@~1.0.1
diff --git a/lib/response.js b/lib/response.js
index f3f043f5cd..b852a60e2f 100644
--- a/lib/response.js
+++ b/lib/response.js
@@ -717,9 +717,14 @@ res.header = function header(field, val) {
       : String(val);
 
     // add charset to content-type
-    if (field.toLowerCase() === 'content-type' && !charsetRegExp.test(value)) {
-      var charset = mime.charsets.lookup(value.split(';')[0]);
-      if (charset) value += '; charset=' + charset.toLowerCase();
+    if (field.toLowerCase() === 'content-type') {
+      if (Array.isArray(value)) {
+        throw new TypeError('Content-Type cannot be set to an Array');
+      }
+      if (!charsetRegExp.test(value)) {
+        var charset = mime.charsets.lookup(value.split(';')[0]);
+        if (charset) value += '; charset=' + charset.toLowerCase();
+      }
     }
 
     this.setHeader(field, value);
diff --git a/test/res.set.js b/test/res.set.js
index b15bc5d7e3..e46d123947 100644
--- a/test/res.set.js
+++ b/test/res.set.js
@@ -73,6 +73,19 @@ describe('res', function(){
       .expect('Content-Type', 'text/html; charset=lol')
       .expect(200, done);
     })
+
+    it('should throw when Content-Type is an array', function (done) {
+      var app = express()
+
+      app.use(function (req, res) {
+        res.set('Content-Type', ['text/html'])
+        res.end()
+      });
+
+      request(app)
+      .get('/')
+      .expect(500, /TypeError: Content-Type cannot be set to an Array/, done)
+    })
   })
 
   describe('.set(object)', function(){