diff --git a/extensions/resteasy-reactive/rest-client-reactive/deployment/src/test/java/io/quarkus/rest/client/reactive/headers/UserAgentTest.java b/extensions/resteasy-reactive/rest-client-reactive/deployment/src/test/java/io/quarkus/rest/client/reactive/headers/UserAgentTest.java
index 7ea164cbc1fdc..6f85bd51de27f 100644
--- a/extensions/resteasy-reactive/rest-client-reactive/deployment/src/test/java/io/quarkus/rest/client/reactive/headers/UserAgentTest.java
+++ b/extensions/resteasy-reactive/rest-client-reactive/deployment/src/test/java/io/quarkus/rest/client/reactive/headers/UserAgentTest.java
@@ -10,6 +10,7 @@
 import jakarta.ws.rs.Path;
 
 import org.eclipse.microprofile.rest.client.RestClientBuilder;
+import org.eclipse.microprofile.rest.client.annotation.ClientHeaderParam;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.RegisterExtension;
 
@@ -36,6 +37,18 @@ void testHeaderOverride() {
         assertThat(client.callWithUserAgent("custom-agent")).isEqualTo("custom-agent");
     }
 
+    @Test
+    void testHeadersWithImplicitValue() {
+        ClientWithAnnotation client = RestClientBuilder.newBuilder().baseUri(baseUri).build(ClientWithAnnotation.class);
+        assertThat(client.callWithImplicitValue()).isEqualTo("Annotated");
+    }
+
+    @Test
+    void testHeadersWithExplicitValue() {
+        ClientWithAnnotation client = RestClientBuilder.newBuilder().baseUri(baseUri).build(ClientWithAnnotation.class);
+        assertThat(client.callWithExplicitValue("custom-agent")).isEqualTo("custom-agent");
+    }
+
     @Path("/")
     @ApplicationScoped
     public static class Resource {
@@ -56,4 +69,16 @@ public interface Client {
         String callWithUserAgent(@HeaderParam("User-AgenT") String userAgent);
     }
 
+    @ClientHeaderParam(name = "User-Agent", value = "Annotated")
+    public interface ClientWithAnnotation {
+
+        @Path("/")
+        @GET
+        String callWithImplicitValue();
+
+        @Path("/")
+        @GET
+        String callWithExplicitValue(@HeaderParam("User-Agent") String userAgent);
+    }
+
 }
diff --git a/extensions/resteasy-reactive/rest-client-reactive/runtime/src/main/java/io/quarkus/rest/client/reactive/runtime/HeaderFillerUtil.java b/extensions/resteasy-reactive/rest-client-reactive/runtime/src/main/java/io/quarkus/rest/client/reactive/runtime/HeaderFillerUtil.java
index 632afb5cef99a..bebe8e1160a0c 100644
--- a/extensions/resteasy-reactive/rest-client-reactive/runtime/src/main/java/io/quarkus/rest/client/reactive/runtime/HeaderFillerUtil.java
+++ b/extensions/resteasy-reactive/rest-client-reactive/runtime/src/main/java/io/quarkus/rest/client/reactive/runtime/HeaderFillerUtil.java
@@ -6,6 +6,8 @@
 import jakarta.ws.rs.core.HttpHeaders;
 import jakarta.ws.rs.core.MultivaluedMap;
 
+import org.jboss.resteasy.reactive.client.impl.RestClientRequestContext;
+
 @SuppressWarnings("unused")
 public final class HeaderFillerUtil {
 
@@ -27,6 +29,8 @@ public static boolean shouldAddHeader(String name, MultivaluedMap<String, String
                 // if the header is the Content-Type, then we should update if its current value equals what determined at build time (and therefore no other code has changed it)
                 return existingValue.equals(defaultContentType);
             }
+        } else if (HttpHeaders.USER_AGENT.equals(name)) {
+            return RestClientRequestContext.DEFAULT_USER_AGENT_VALUE.equals(existingValue);
         } else {
             return false;
         }
diff --git a/independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/ClientBuilderImpl.java b/independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/ClientBuilderImpl.java
index 8cabb175d17ff..12e4381f7088d 100644
--- a/independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/ClientBuilderImpl.java
+++ b/independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/ClientBuilderImpl.java
@@ -75,7 +75,7 @@ public class ClientBuilderImpl extends ClientBuilder {
     private MultiQueryParamMode multiQueryParamMode;
 
     private ClientLogger clientLogger = new DefaultClientLogger();
-    private String userAgent = "Resteasy Reactive Client";
+    private String userAgent = RestClientRequestContext.DEFAULT_USER_AGENT_VALUE;
 
     private boolean enableCompression;
 
diff --git a/independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/RestClientRequestContext.java b/independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/RestClientRequestContext.java
index 1f2cd578af864..a2f7e9fba9102 100644
--- a/independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/RestClientRequestContext.java
+++ b/independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/RestClientRequestContext.java
@@ -58,6 +58,7 @@ public class RestClientRequestContext extends AbstractResteasyReactiveContext<Re
     public static final String INVOKED_METHOD_PROP = "org.eclipse.microprofile.rest.client.invokedMethod";
     public static final String INVOKED_METHOD_PARAMETERS_PROP = "io.quarkus.rest.client.invokedMethodParameters";
     public static final String DEFAULT_CONTENT_TYPE_PROP = "io.quarkus.rest.client.defaultContentType";
+    public static final String DEFAULT_USER_AGENT_VALUE = "Resteasy Reactive Client";
     private static final String TMP_FILE_PATH_KEY = "tmp_file_path";
 
     static final MediaType IGNORED_MEDIA_TYPE = new MediaType("ignored", "ignored");