diff --git a/httpclient.go b/httpclient.go
index 8f66c3b..7f031d1 100644
--- a/httpclient.go
+++ b/httpclient.go
@@ -52,7 +52,7 @@ type Client struct {
 	username string
 	password string
 
-	// custom http header
+	// custom http header(s)
 	header http.Header
 
 	Marshaler   MarshalerFunc
@@ -191,7 +191,8 @@ func WithContentType(ct string) Opt {
 }
 
 // WithHeader is a client option for setting custom http header(s) for each request
-// Content-Type and Accept headers will always be overwritten by the clients ContentType setting
+// Content-Type and Accept headers will be appended by the clients ContentType setting
+// Authorization header is overwritten if WithUsername/WithPassowrd was used to setup the client
 func WithHeader(header http.Header) Opt {
 	return func(c *Client) error {
 		c.header = header
@@ -225,13 +226,13 @@ func (c *Client) NewRequest(method, urlStr string, body interface{}) (*http.Requ
 		return nil, err
 	}
 
-	if len(c.username) > 0 && len(c.password) > 0 {
-		req.SetBasicAuth(c.username, c.password)
-	}
-
 	if c.header != nil {
 		req.Header = c.header
 	}
+
+	if len(c.username) > 0 && len(c.password) > 0 {
+		req.SetBasicAuth(c.username, c.password)
+	}
 	req.Header.Add("Content-Type", contentType)
 	req.Header.Add("Accept", contentType)
 
@@ -298,7 +299,7 @@ func (c *Client) Do(ctx context.Context, req *http.Request, v interface{}) (*htt
 	}()
 
 	if c.ResponseCallback == nil {
-		panic("CheckResponse is  nil")
+		panic("ResponseCallback is nil")
 	}
 
 	resp, err = c.ResponseCallback(resp)
diff --git a/httpclient_test.go b/httpclient_test.go
index 813b638..1a37c2b 100644
--- a/httpclient_test.go
+++ b/httpclient_test.go
@@ -123,6 +123,25 @@ func TestClient(t *testing.T) {
 		assert.Contains(t, req.Header, "Accept")
 	})
 
+	t.Run("new client with headers and basic auth", func(t *testing.T) {
+		username := "user1"
+		password := "123456"
+		fakeAuthHeader := http.Header{
+			"Authorization": []string{"fake"},
+		}
+
+		c, err := New(baseurl, WithHeader(fakeAuthHeader), WithUsername(username), WithPassword(password))
+		assert.Nil(t, err)
+		assert.NotNil(t, c)
+
+		req, err := c.NewRequest(http.MethodGet, "/test", nil)
+		assert.Nil(t, err)
+		user, passwd, ok := req.BasicAuth()
+		assert.True(t, ok)
+		assert.Equal(t, user, username)
+		assert.Equal(t, passwd, passwd)
+	})
+
 	t.Run("new client valid baseurl valid HTTP client", func(t *testing.T) {
 		httpC := &http.Client{}
 		c, err := New(baseurl, WithHTTPClient(httpC))