diff --git a/extensions/resteasy-reactive/rest-client-reactive/deployment/src/test/java/io/quarkus/rest/client/reactive/provider/EntitySettingRequestFilterTest.java b/extensions/resteasy-reactive/rest-client-reactive/deployment/src/test/java/io/quarkus/rest/client/reactive/provider/EntitySettingRequestFilterTest.java
new file mode 100644
index 0000000000000..18fe86069f6c7
--- /dev/null
+++ b/extensions/resteasy-reactive/rest-client-reactive/deployment/src/test/java/io/quarkus/rest/client/reactive/provider/EntitySettingRequestFilterTest.java
@@ -0,0 +1,74 @@
+package io.quarkus.rest.client.reactive.provider;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.io.IOException;
+import java.net.URI;
+
+import jakarta.ws.rs.POST;
+import jakarta.ws.rs.Path;
+import jakarta.ws.rs.client.ClientRequestContext;
+import jakarta.ws.rs.client.ClientRequestFilter;
+
+import org.eclipse.microprofile.rest.client.RestClientBuilder;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+import io.quarkus.test.QuarkusUnitTest;
+import io.quarkus.test.common.http.TestHTTPResource;
+
+public class EntitySettingRequestFilterTest {
+
+    @RegisterExtension
+    static final QuarkusUnitTest config = new QuarkusUnitTest()
+            .withApplicationRoot((jar) -> jar.addClasses(Resource.class, Client.class, EntityRequestFilter.class));
+
+    @TestHTTPResource
+    URI baseUri;
+
+    @Test
+    void testNullEntity() {
+        Client client = RestClientBuilder.newBuilder().baseUri(baseUri).register(new EntityRequestFilter(null))
+                .build(Client.class);
+        assertThat(client.call("ignored")).isEqualTo("null");
+    }
+
+    @Test
+    void testNonNullEntity() {
+        Client client = RestClientBuilder.newBuilder().baseUri(baseUri).register(new EntityRequestFilter("foo"))
+                .build(Client.class);
+        assertThat(client.call("ignored")).isEqualTo("foo");
+    }
+
+    @Path("/")
+    public static class Resource {
+        @POST
+        public String returnHeaders(String body) {
+            if ((body == null) || body.isEmpty()) {
+                return "null";
+            }
+            return body;
+        }
+    }
+
+    public interface Client {
+
+        @Path("/")
+        @POST
+        String call(String body);
+    }
+
+    public static class EntityRequestFilter implements ClientRequestFilter {
+
+        private final String entity;
+
+        public EntityRequestFilter(String entity) {
+            this.entity = entity;
+        }
+
+        @Override
+        public void filter(ClientRequestContext context) throws IOException {
+            context.setEntity(entity);
+        }
+    }
+}
diff --git a/independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/ClientRequestContextImpl.java b/independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/ClientRequestContextImpl.java
index eb653ee587544..f1b2017f27c82 100644
--- a/independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/ClientRequestContextImpl.java
+++ b/independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/ClientRequestContextImpl.java
@@ -171,8 +171,12 @@ public Locale getLanguage() {
 
     @Override
     public MediaType getMediaType() {
+        if (restClientRequestContext.entity == null) {
+            return null;
+        }
         // those come from the entity
-        return restClientRequestContext.entity != null ? restClientRequestContext.entity.getMediaType() : null;
+        return restClientRequestContext.entity.getMediaType() == RestClientRequestContext.IGNORED_MEDIA_TYPE ? null
+                : restClientRequestContext.entity.getMediaType();
     }
 
     @Override
@@ -515,12 +519,8 @@ private boolean isContentType(Object key) {
         }
 
         private String mediaType() {
-            Entity<?> entity = restClientRequestContext.entity;
-            return entity == null
-                    ? null
-                    : entity.getMediaType() == null
-                            ? null
-                            : entity.getMediaType().toString();
+            MediaType mediaType = getMediaType();
+            return mediaType == null ? null : mediaType.toString();
         }
     }
 }
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 59e89940f428c..3fb35e41152e7 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
@@ -60,6 +60,8 @@ public class RestClientRequestContext extends AbstractResteasyReactiveContext<Re
     public static final String DEFAULT_CONTENT_TYPE_PROP = "io.quarkus.rest.client.defaultContentType";
     private static final String TMP_FILE_PATH_KEY = "tmp_file_path";
 
+    static final MediaType IGNORED_MEDIA_TYPE = new MediaType("ignored", "ignored");
+
     private final HttpClient httpClient;
     // Changeable by the request filter
     String httpMethod;
@@ -273,7 +275,14 @@ public Buffer writeEntity(Entity<?> entity, MultivaluedMap<String, String> heade
     }
 
     public void setEntity(Object entity, Annotation[] annotations, MediaType mediaType) {
-        this.entity = Entity.entity(entity, mediaType, annotations);
+        if (entity == null) {
+            this.entity = null;
+        } else {
+            if (mediaType == null) {
+                mediaType = IGNORED_MEDIA_TYPE; // we need this in order to avoid getting IAE from Variant...
+            }
+            this.entity = Entity.entity(entity, mediaType, annotations);
+        }
     }
 
     public CompletableFuture<ResponseImpl> getResult() {