diff --git a/google-cloud-spanner/src/main/java/com/google/cloud/spanner/spi/v1/GapicSpannerRpc.java b/google-cloud-spanner/src/main/java/com/google/cloud/spanner/spi/v1/GapicSpannerRpc.java
index 807eac6f11b..608d9e23d53 100644
--- a/google-cloud-spanner/src/main/java/com/google/cloud/spanner/spi/v1/GapicSpannerRpc.java
+++ b/google-cloud-spanner/src/main/java/com/google/cloud/spanner/spi/v1/GapicSpannerRpc.java
@@ -77,7 +77,6 @@
 import com.google.common.base.MoreObjects;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
-import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.util.concurrent.RateLimiter;
 import com.google.common.util.concurrent.ThreadFactoryBuilder;
@@ -161,6 +160,7 @@
 import java.net.URLDecoder;
 import java.nio.charset.StandardCharsets;
 import java.util.Comparator;
+import java.util.HashMap;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
@@ -244,6 +244,8 @@ private void awaitTermination() throws InterruptedException {
   private static final int GRPC_KEEPALIVE_SECONDS = 2 * 60;
   private static final String USER_AGENT_KEY = "user-agent";
   private static final String CLIENT_LIBRARY_LANGUAGE = "spanner-java";
+  public static final String DEFAULT_USER_AGENT =
+      CLIENT_LIBRARY_LANGUAGE + "/" + GaxProperties.getLibraryVersion(GapicSpannerRpc.class);
 
   private final ManagedInstantiatingExecutorProvider executorProvider;
   private boolean rpcIsClosed;
@@ -305,18 +307,11 @@ public GapicSpannerRpc(final SpannerOptions options) {
                 GaxGrpcProperties.getGrpcTokenName(), GaxGrpcProperties.getGrpcVersion())
             .build();
 
-    HeaderProvider mergedHeaderProvider = options.getMergedHeaderProvider(internalHeaderProvider);
-    Map<String, String> headersWithUserAgent =
-        ImmutableMap.<String, String>builder()
-            .put(
-                USER_AGENT_KEY,
-                CLIENT_LIBRARY_LANGUAGE
-                    + "/"
-                    + GaxProperties.getLibraryVersion(GapicSpannerRpc.class))
-            .putAll(mergedHeaderProvider.getHeaders())
-            .build();
+    final HeaderProvider mergedHeaderProvider =
+        options.getMergedHeaderProvider(internalHeaderProvider);
     final HeaderProvider headerProviderWithUserAgent =
-        FixedHeaderProvider.create(headersWithUserAgent);
+        headerProviderWithUserAgentFrom(mergedHeaderProvider);
+
     this.metadataProvider =
         SpannerMetadataProvider.create(
             headerProviderWithUserAgent.getHeaders(),
@@ -494,6 +489,16 @@ public <RequestT, ResponseT> UnaryCallable<RequestT, ResponseT> createUnaryCalla
     }
   }
 
+  private static HeaderProvider headerProviderWithUserAgentFrom(HeaderProvider headerProvider) {
+    final Map<String, String> headersWithUserAgent = new HashMap<>(headerProvider.getHeaders());
+    final String userAgent = headersWithUserAgent.get(USER_AGENT_KEY);
+    headersWithUserAgent.put(
+        USER_AGENT_KEY,
+        userAgent == null ? DEFAULT_USER_AGENT : userAgent + " " + DEFAULT_USER_AGENT);
+
+    return FixedHeaderProvider.create(headersWithUserAgent);
+  }
+
   private static void checkEmulatorConnection(
       SpannerOptions options,
       TransportChannelProvider channelProvider,
diff --git a/google-cloud-spanner/src/test/java/com/google/cloud/spanner/spi/v1/GapicSpannerRpcTest.java b/google-cloud-spanner/src/test/java/com/google/cloud/spanner/spi/v1/GapicSpannerRpcTest.java
index 84aaa91bcf5..5a9dec72edc 100644
--- a/google-cloud-spanner/src/test/java/com/google/cloud/spanner/spi/v1/GapicSpannerRpcTest.java
+++ b/google-cloud-spanner/src/test/java/com/google/cloud/spanner/spi/v1/GapicSpannerRpcTest.java
@@ -24,7 +24,9 @@
 import static org.junit.Assume.assumeTrue;
 
 import com.google.api.core.ApiFunction;
+import com.google.api.gax.core.GaxProperties;
 import com.google.api.gax.rpc.ApiCallContext;
+import com.google.api.gax.rpc.HeaderProvider;
 import com.google.auth.oauth2.AccessToken;
 import com.google.auth.oauth2.OAuth2Credentials;
 import com.google.cloud.spanner.DatabaseAdminClient;
@@ -151,6 +153,8 @@ public class GapicSpannerRpcTest {
   private Server server;
   private InetSocketAddress address;
   private final Map<SpannerRpc.Option, Object> optionsMap = new HashMap<>();
+  private Metadata seenHeaders;
+  private String defaultUserAgent;
 
   @BeforeClass
   public static void checkNotEmulator() {
@@ -161,6 +165,7 @@ public static void checkNotEmulator() {
 
   @Before
   public void startServer() throws IOException {
+    defaultUserAgent = "spanner-java/" + GaxProperties.getLibraryVersion(GapicSpannerRpc.class);
     mockSpanner = new MockSpannerServiceImpl();
     mockSpanner.setAbortProbability(0.0D); // We don't want any unpredictable aborted transactions.
     mockSpanner.putStatementResult(StatementResult.query(SELECT1AND2, SELECT1_RESULTSET));
@@ -183,6 +188,7 @@ public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(
                       ServerCall<ReqT, RespT> call,
                       Metadata headers,
                       ServerCallHandler<ReqT, RespT> next) {
+                    seenHeaders = headers;
                     String auth =
                         headers.get(Key.of("authorization", Metadata.ASCII_STRING_MARSHALLER));
                     assertThat(auth).isEqualTo("Bearer " + VARIABLE_OAUTH_TOKEN);
@@ -502,6 +508,46 @@ public void testAdminRequestsLimitExceededRetryAlgorithm() {
     assertThat(alg.shouldRetry(new Exception("random exception"), null)).isFalse();
   }
 
+  @Test
+  public void testDefaultUserAgent() {
+    final SpannerOptions options = createSpannerOptions();
+    final Spanner spanner = options.getService();
+    final DatabaseClient databaseClient =
+        spanner.getDatabaseClient(DatabaseId.of("[PROJECT]", "[INSTANCE]", "[DATABASE]"));
+
+    try (final ResultSet rs = databaseClient.singleUse().executeQuery(SELECT1AND2)) {
+      rs.next();
+    }
+
+    assertThat(seenHeaders.get(Key.of("user-agent", Metadata.ASCII_STRING_MARSHALLER)))
+        .contains(defaultUserAgent);
+  }
+
+  @Test
+  public void testCustomUserAgent() {
+    final HeaderProvider userAgentHeaderProvider =
+        new HeaderProvider() {
+          @Override
+          public Map<String, String> getHeaders() {
+            final Map<String, String> headers = new HashMap<>();
+            headers.put("user-agent", "test-agent");
+            return headers;
+          }
+        };
+    final SpannerOptions options =
+        createSpannerOptions().toBuilder().setHeaderProvider(userAgentHeaderProvider).build();
+    final Spanner spanner = options.getService();
+    final DatabaseClient databaseClient =
+        spanner.getDatabaseClient(DatabaseId.of("[PROJECT]", "[INSTANCE]", "[DATABASE]"));
+
+    try (final ResultSet rs = databaseClient.singleUse().executeQuery(SELECT1AND2)) {
+      rs.next();
+    }
+
+    assertThat(seenHeaders.get(Key.of("user-agent", Metadata.ASCII_STRING_MARSHALLER)))
+        .contains("test-agent " + defaultUserAgent);
+  }
+
   @SuppressWarnings("rawtypes")
   private SpannerOptions createSpannerOptions() {
     String endpoint = address.getHostString() + ":" + server.getPort();