diff --git a/handler.go b/handler.go
index a61a872..53a9f3c 100644
--- a/handler.go
+++ b/handler.go
@@ -138,6 +138,9 @@ func (h *Handler) ContextHandler(ctx context.Context, w http.ResponseWriter, r *
 		}
 	}
 
+	// use proper JSON Header
+	w.Header().Add("Content-Type", "application/json")
+
 	if h.pretty {
 		w.WriteHeader(http.StatusOK)
 		buff, _ := json.MarshalIndent(result, "", "\t")
diff --git a/handler_test.go b/handler_test.go
index 7c8a60b..ea73d2a 100644
--- a/handler_test.go
+++ b/handler_test.go
@@ -10,10 +10,10 @@ import (
 	"strings"
 	"testing"
 
+	"context"
 	"github.com/graphql-go/graphql"
 	"github.com/graphql-go/graphql/testutil"
 	"github.com/graphql-go/handler"
-	"context"
 )
 
 func decodeResponse(t *testing.T, recorder *httptest.ResponseRecorder) *graphql.Result {