diff --git a/google/cloud/internal/populate_grpc_options.cc b/google/cloud/internal/populate_grpc_options.cc
index 3d547b9ee787c..0d946748ffbcb 100644
--- a/google/cloud/internal/populate_grpc_options.cc
+++ b/google/cloud/internal/populate_grpc_options.cc
@@ -29,7 +29,8 @@ Options PopulateGrpcOptions(Options opts, std::string const& emulator_env_var) {
       opts.set<GrpcCredentialOption>(grpc::InsecureChannelCredentials());
     }
   }
-  if (!opts.has<GrpcCredentialOption>()) {
+  if (!opts.has<GrpcCredentialOption>() &&
+      !opts.has<UnifiedCredentialsOption>()) {
     opts.set<GrpcCredentialOption>(grpc::GoogleDefaultCredentials());
   }
   if (!opts.has<GrpcTracingOptionsOption>()) {