diff --git a/http/handler.go b/http/handler.go
index 8cc059035..3226eee50 100644
--- a/http/handler.go
+++ b/http/handler.go
@@ -964,10 +964,12 @@ func (h *Handler) readURLQueryRequest(r *http.Request) (*pilosa.QueryRequest, er
 }
 
 // writeQueryResponse writes the response from the executor to w.
-func (h *Handler) writeQueryResponse(w io.Writer, r *http.Request, resp *pilosa.QueryResponse) error {
+func (h *Handler) writeQueryResponse(w http.ResponseWriter, r *http.Request, resp *pilosa.QueryResponse) error {
 	if !validHeaderAcceptJSON(r.Header) {
+		w.Header().Set("Content-Type", "application/protobuf")
 		return h.writeProtobufQueryResponse(w, resp)
 	}
+	w.Header().Set("Content-Type", "application/json")
 	return h.writeJSONQueryResponse(w, resp)
 }
 
diff --git a/server/handler_test.go b/server/handler_test.go
index ed7a2bed6..f45aa2422 100644
--- a/server/handler_test.go
+++ b/server/handler_test.go
@@ -248,6 +248,8 @@ func TestHandler_Endpoints(t *testing.T) {
 			t.Fatalf("unexpected status code: %d", w.Code)
 		} else if body := w.Body.String(); body != `{"results":[2]}`+"\n" {
 			t.Fatalf("unexpected body: %q", body)
+		} else if w.Header().Get("Content-Type") != "application/json" {
+			t.Fatalf("unexpected header: %q", w.Header().Get("Content-Type"))
 		}
 
 	})
@@ -286,6 +288,8 @@ func TestHandler_Endpoints(t *testing.T) {
 			t.Fatal(err)
 		} else if rt, ok := resp.Results[0].(uint64); !ok || rt != 3 {
 			t.Fatalf("unexpected response type: %#v", resp.Results[0])
+		} else if w.Header().Get("Content-Type") != "application/protobuf" {
+			t.Fatalf("unexpected header: %q", w.Header().Get("Content-Type"))
 		}
 	})