diff --git a/exporters/otlp/BUILD b/exporters/otlp/BUILD
index 1234567..abcdefg 100644
--- a/exporters/otlp/BUILD
+++ b/exporters/otlp/BUILD
@@ -42,6 +42,9 @@ cc_library(
         "include/opentelemetry/exporters/otlp/protobuf_include_prefix.h",
         "include/opentelemetry/exporters/otlp/protobuf_include_suffix.h",
     ],
+    defines = [
+        "ENABLE_OTLP_GRPC_SSL_MTLS_PREVIEW",
+    ],
     strip_include_prefix = "include",
     tags = [
         "otlp",