@@ -166,6 +166,7 @@
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
+import java.util.Map.Entry;
 import java.util.Set;
 import java.util.concurrent.Callable;
 import java.util.concurrent.CancellationException;
@@ -493,7 +494,14 @@ 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);
+String userAgent = null;
+for (Entry<String, String> entry : headersWithUserAgent.entrySet()) {
+if (entry.getKey().equalsIgnoreCase(USER_AGENT_KEY)) {
+userAgent = entry.getValue();
+headersWithUserAgent.remove(entry.getKey());
+break;
+}
+}
 headersWithUserAgent.put(
 USER_AGENT_KEY,
 userAgent == null ? DEFAULT_USER_AGENT : userAgent + " " + DEFAULT_USER_AGENT);

@@ -509,27 +509,29 @@ public void testDefaultUserAgent() {
 
 @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();
-try (Spanner spanner = options.getService()) {
-final DatabaseClient databaseClient =
-spanner.getDatabaseClient(DatabaseId.of("[PROJECT]", "[INSTANCE]", "[DATABASE]"));
+for (String headerId : new String[] {"user-agent", "User-Agent", "USER-AGENT"}) {
+final HeaderProvider userAgentHeaderProvider =
+new HeaderProvider() {
+@Override
+public Map<String, String> getHeaders() {
+final Map<String, String> headers = new HashMap<>();
+headers.put(headerId, "test-agent");
+return headers;
+}
+};
+final SpannerOptions options =
+createSpannerOptions().toBuilder().setHeaderProvider(userAgentHeaderProvider).build();
+try (Spanner spanner = options.getService()) {
+final DatabaseClient databaseClient =
+spanner.getDatabaseClient(DatabaseId.of("[PROJECT]", "[INSTANCE]", "[DATABASE]"));
+
+try (final ResultSet rs = databaseClient.singleUse().executeQuery(SELECT1AND2)) {
+rs.next();
+}
 
-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);
 }
-
-assertThat(seenHeaders.get(Key.of("user-agent", Metadata.ASCII_STRING_MARSHALLER)))
-.contains("test-agent " + defaultUserAgent);
 }
 }