diff --git a/api/api_test.go b/api/api_test.go
index 0048ecdfe67..dbdb62049a1 100644
--- a/api/api_test.go
+++ b/api/api_test.go
@@ -10,6 +10,7 @@ import (
 	"net/url"
 	"os"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -538,3 +539,36 @@ func TestCloneHttpClient(t *testing.T) {
 	})
 
 }
+
+func TestClient_HeaderRaceCondition(t *testing.T) {
+	require := require.New(t)
+
+	conf := DefaultConfig()
+	conf.Headers = map[string][]string{
+		"test-header": {"a"},
+	}
+	client, err := NewClient(conf)
+	require.NoError(err)
+
+	wg := sync.WaitGroup{}
+	wg.Add(2)
+
+	go func() {
+		for i := 0; i < 500; i++ {
+			req, err := client.newRequest("GET", "/any/path/will/do")
+			require.NoError(err)
+			_, _ = req.toHTTP()
+		}
+		wg.Done()
+	}()
+	go func() {
+		for i := 0; i < 500; i++ {
+			req, err := client.newRequest("GET", "/any/path/will/do")
+			require.NoError(err)
+			_, _ = req.toHTTP()
+		}
+		wg.Done()
+	}()
+
+	wg.Wait()
+}