diff --git a/BUILD.gn b/BUILD.gn
index bd17202..8653d56 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -32,6 +32,8 @@
 }
 
 source_set("gtest") {
+  testonly = true
+
   sources = [
     "include/gtest/gtest-death-test.h",
     "include/gtest/gtest-message.h",