diff --git a/core/fdrm/BUILD.gn b/core/fdrm/BUILD.gn
index 8e79c14..0b14d7f 100644
--- a/core/fdrm/BUILD.gn
+++ b/core/fdrm/BUILD.gn
@@ -12,9 +12,13 @@
     "fx_crypt_aes.cpp",
     "fx_crypt_sha.cpp",
   ]
+  cflags = []
   configs += [ "../../:pdfium_strict_config" ]
   deps = [ "../fxcrt" ]
   visibility = [ "../../*" ]
+  if (is_clang) {
+    cflags += [ "-Wshorten-64-to-32" ]
+  }
 }
 
 pdfium_unittest_source_set("unittests") {