diff --git a/include/grpc/impl/codegen/sync_custom.h b/include/grpc/impl/codegen/sync_custom.h
index f7f7d121d82..0840ad26bfa 100644
--- a/include/grpc/impl/codegen/sync_custom.h
+++ b/include/grpc/impl/codegen/sync_custom.h
@@ -23,10 +23,14 @@
 
 /* Users defining GPR_CUSTOM_SYNC need to define the following macros. */
 
+#ifdef GPR_CUSTOM_SYNC
+
 typedef GPR_CUSTOM_MU_TYPE gpr_mu;
 typedef GPR_CUSTOM_CV_TYPE gpr_cv;
 typedef GPR_CUSTOM_ONCE_TYPE gpr_once;
 
 #define GPR_ONCE_INIT GPR_CUSTOM_ONCE_INIT
 
+#endif
+
 #endif /* GRPC_IMPL_CODEGEN_SYNC_CUSTOM_H */