diff --git a/google/cloud/internal/curl_impl.cc b/google/cloud/internal/curl_impl.cc
index 896f060f1e7bb..26998dbd6988c 100644
--- a/google/cloud/internal/curl_impl.cc
+++ b/google/cloud/internal/curl_impl.cc
@@ -212,8 +212,9 @@ CurlImpl::CurlImpl(CurlHandle handle,
   socket_options_.send_buffer_size_ =
       options.get<MaximumCurlSocketSendSizeOption>();
 
-  auto const& agents = options.get<UserAgentProductsOption>();
-  user_agent_ = absl::StrCat(absl::StrJoin(agents, " "), UserAgentSuffix());
+  auto agents = options.get<UserAgentProductsOption>();
+  agents.push_back(UserAgentSuffix());
+  user_agent_ = absl::StrJoin(agents, " ");
 
   http_version_ = options.get<HttpVersionOption>();
 
diff --git a/google/cloud/internal/curl_rest_client_integration_test.cc b/google/cloud/internal/curl_rest_client_integration_test.cc
index 32903c84cf725..39c493e5a55b0 100644
--- a/google/cloud/internal/curl_rest_client_integration_test.cc
+++ b/google/cloud/internal/curl_rest_client_integration_test.cc
@@ -22,6 +22,7 @@
 #include "google/cloud/testing_util/contains_once.h"
 #include "google/cloud/testing_util/status_matchers.h"
 #include "absl/strings/match.h"
+#include "absl/strings/str_split.h"
 #include <gmock/gmock.h>
 #include <nlohmann/json.hpp>
 
@@ -38,6 +39,7 @@ using ::testing::Eq;
 using ::testing::HasSubstr;
 using ::testing::Not;
 using ::testing::Pair;
+using ::testing::StartsWith;
 
 class RestClientIntegrationTest : public ::testing::Test {
  protected:
@@ -554,8 +556,10 @@ TEST_F(RestClientIntegrationTest, PerRequestOptions) {
   ASSERT_TRUE(parsed_response.is_object()) << "body=" << *body;
   auto headers = parsed_response.find("headers");
   ASSERT_TRUE(headers != parsed_response.end()) << "body=" << *body;
-  EXPECT_THAT(headers->value("User-Agent", ""), HasSubstr(p1));
-  EXPECT_THAT(headers->value("User-Agent", ""), HasSubstr(p2));
+  auto const products = std::vector<std::string>(
+      absl::StrSplit(headers->value("User-Agent", ""), ' '));
+  EXPECT_THAT(products, AllOf(Contains(p1), Contains(p2),
+                              Contains(StartsWith("gcloud-cpp/"))));
 }
 
 }  // namespace
diff --git a/google/cloud/storage/tests/curl_request_integration_test.cc b/google/cloud/storage/tests/curl_request_integration_test.cc
index f151e66fc3451..37367d161422a 100644
--- a/google/cloud/storage/tests/curl_request_integration_test.cc
+++ b/google/cloud/storage/tests/curl_request_integration_test.cc
@@ -346,7 +346,7 @@ TEST(CurlRequestTest, UserAgent) {
         HttpBinEndpoint() + "/headers",
         storage::internal::GetDefaultCurlHandleFactory());
     auto options = google::cloud::Options{}.set<UserAgentProductsOption>(
-        {"test-user-agent-prefix"});
+        {"test-user-agent-prefix-1", "test-user-agent-prefix-2"});
     builder.ApplyClientOptions(options);
     builder.AddHeader("Accept: application/json");
     builder.AddHeader("charsets: utf-8");
@@ -357,11 +357,13 @@ TEST(CurlRequestTest, UserAgent) {
   ASSERT_STATUS_OK(response);
   ASSERT_EQ(200, response->status_code) << "response=" << *response;
   auto payload = nlohmann::json::parse(response->payload);
-  ASSERT_EQ(1U, payload.count("headers"));
-  auto headers = payload["headers"];
-  EXPECT_THAT(headers.value("User-Agent", ""),
-              HasSubstr("test-user-agent-prefix"));
-  EXPECT_THAT(headers.value("User-Agent", ""), HasSubstr("gcloud-cpp/"));
+  ASSERT_TRUE(payload.is_object()) << "payload=" << response->payload;
+  ASSERT_TRUE(payload.contains("headers")) << "payload=" << response->payload;
+  auto const products = std::vector<std::string>(
+      absl::StrSplit(payload["headers"].value("User-Agent", ""), ' '));
+  EXPECT_THAT(products, AllOf(Contains("test-user-agent-prefix-1"),
+                              Contains("test-user-agent-prefix-2"),
+                              Contains(StartsWith("gcloud-cpp/"))));
 }
 
 #if CURL_AT_LEAST_VERSION(7, 43, 0)