diff --git a/spring-web/src/main/java/org/springframework/http/converter/protobuf/ExtensionRegistryInitializer.java b/spring-web/src/main/java/org/springframework/http/converter/protobuf/ExtensionRegistryInitializer.java
index decb36208d..95b5d430b2 100644
--- a/spring-web/src/main/java/org/springframework/http/converter/protobuf/ExtensionRegistryInitializer.java
+++ b/spring-web/src/main/java/org/springframework/http/converter/protobuf/ExtensionRegistryInitializer.java
@@ -25,10 +25,13 @@ import com.google.protobuf.ExtensionRegistry;
  * <p>This interface provides a facility to populate the {@code ExtensionRegistry}.
  *
  * @author Alex Antonov
+ * @author Sebastien Deleuze
  * @since 4.1
  * @see <a href="https://developers.google.com/protocol-buffers/docs/reference/java/com/google/protobuf/ExtensionRegistry">
  * com.google.protobuf.ExtensionRegistry</a>
+ * @deprecated as of Spring Framework 5.1, use {@link ExtensionRegistry} based contructors instead
  */
+@Deprecated
 public interface ExtensionRegistryInitializer {
 
 	/**
diff --git a/spring-web/src/main/java/org/springframework/http/converter/protobuf/ProtobufHttpMessageConverter.java b/spring-web/src/main/java/org/springframework/http/converter/protobuf/ProtobufHttpMessageConverter.java
index 585b0edfde..75ece8284d 100644
--- a/spring-web/src/main/java/org/springframework/http/converter/protobuf/ProtobufHttpMessageConverter.java
+++ b/spring-web/src/main/java/org/springframework/http/converter/protobuf/ProtobufHttpMessageConverter.java
@@ -77,6 +77,7 @@ import static org.springframework.http.MediaType.TEXT_PLAIN;
  * @author Alex Antonov
  * @author Brian Clozel
  * @author Juergen Hoeller
+ * @author Sebastien Deleuze
  * @since 4.1
  * @see FormatFactory
  * @see JsonFormat
@@ -107,7 +108,7 @@ public class ProtobufHttpMessageConverter extends AbstractHttpMessageConverter<M
 
 	private static final Map<Class<?>, Method> methodCache = new ConcurrentReferenceHashMap<>();
 
-	private final ExtensionRegistry extensionRegistry = ExtensionRegistry.newInstance();
+	final ExtensionRegistry extensionRegistry;
 
 	@Nullable
 	private final ProtobufFormatSupport protobufFormatSupport;
@@ -117,20 +118,34 @@ public class ProtobufHttpMessageConverter extends AbstractHttpMessageConverter<M
 	 * Construct a new {@code ProtobufHttpMessageConverter}.
 	 */
 	public ProtobufHttpMessageConverter() {
-		this(null);
+		this(null, null);
 	}
 
 	/**
 	 * Construct a new {@code ProtobufHttpMessageConverter} with an
 	 * initializer that allows the registration of message extensions.
 	 * @param registryInitializer an initializer for message extensions
+	 * @deprecated as of Spring Framework 5.1, use {@link #ProtobufHttpMessageConverter(ExtensionRegistry)} instead
 	 */
+	@Deprecated
 	public ProtobufHttpMessageConverter(@Nullable ExtensionRegistryInitializer registryInitializer) {
-		this(null, registryInitializer);
+		this(null, null);
+		if (registryInitializer != null) {
+			registryInitializer.initializeExtensionRegistry(this.extensionRegistry);
+		}
+	}
+
+	/**
+	 * Construct a new {@code ProtobufHttpMessageConverter} with a registry that specifies
+	 * protocol message extensions.
+	 * @param extensionRegistry the registry to populate
+	 */
+	public ProtobufHttpMessageConverter(ExtensionRegistry extensionRegistry) {
+		this(null, extensionRegistry);
 	}
 
 	ProtobufHttpMessageConverter(@Nullable ProtobufFormatSupport formatSupport,
-			@Nullable ExtensionRegistryInitializer registryInitializer) {
+			@Nullable ExtensionRegistry extensionRegistry) {
 
 		if (formatSupport != null) {
 			this.protobufFormatSupport = formatSupport;
@@ -148,9 +163,7 @@ public class ProtobufHttpMessageConverter extends AbstractHttpMessageConverter<M
 		setSupportedMediaTypes(Arrays.asList(this.protobufFormatSupport != null ?
 				this.protobufFormatSupport.supportedMediaTypes() : new MediaType[] {PROTOBUF, TEXT_PLAIN}));
 
-		if (registryInitializer != null) {
-			registryInitializer.initializeExtensionRegistry(this.extensionRegistry);
-		}
+		this.extensionRegistry = (extensionRegistry == null ? ExtensionRegistry.newInstance() : extensionRegistry);
 	}
 
 
diff --git a/spring-web/src/main/java/org/springframework/http/converter/protobuf/ProtobufJsonFormatHttpMessageConverter.java b/spring-web/src/main/java/org/springframework/http/converter/protobuf/ProtobufJsonFormatHttpMessageConverter.java
index e640459e2c..27106deb53 100644
--- a/spring-web/src/main/java/org/springframework/http/converter/protobuf/ProtobufJsonFormatHttpMessageConverter.java
+++ b/spring-web/src/main/java/org/springframework/http/converter/protobuf/ProtobufJsonFormatHttpMessageConverter.java
@@ -16,6 +16,7 @@
 
 package org.springframework.http.converter.protobuf;
 
+import com.google.protobuf.ExtensionRegistry;
 import com.google.protobuf.util.JsonFormat;
 
 import org.springframework.lang.Nullable;
@@ -32,6 +33,7 @@ import org.springframework.lang.Nullable;
  * with 3.3 or higher recommended.
  *
  * @author Juergen Hoeller
+ * @author Sebastien Deleuze
  * @since 5.0
  * @see JsonFormat#parser()
  * @see JsonFormat#printer()
@@ -44,7 +46,7 @@ public class ProtobufJsonFormatHttpMessageConverter extends ProtobufHttpMessageC
 	 * {@link JsonFormat.Parser} and {@link JsonFormat.Printer} configuration.
 	 */
 	public ProtobufJsonFormatHttpMessageConverter() {
-		this(null,  null, null);
+		this(null,  null, (ExtensionRegistry)null);
 	}
 
 	/**
@@ -56,7 +58,22 @@ public class ProtobufJsonFormatHttpMessageConverter extends ProtobufHttpMessageC
 	public ProtobufJsonFormatHttpMessageConverter(
 			@Nullable JsonFormat.Parser parser, @Nullable JsonFormat.Printer printer) {
 
-		this(parser, printer, null);
+		this(parser, printer, (ExtensionRegistry)null);
+	}
+
+	/**
+	 * Construct a new {@code ProtobufJsonFormatHttpMessageConverter} with the given
+	 * {@link JsonFormat.Parser} and {@link JsonFormat.Printer} configuration, also
+	 * accepting a registry that specifies protocol message extensions.
+	 * @param parser the JSON parser configuration
+	 * @param printer the JSON printer configuration
+	 * @param extensionRegistry the registry to populate
+	 * @since 5.1
+	 */
+	public ProtobufJsonFormatHttpMessageConverter(@Nullable JsonFormat.Parser parser,
+			@Nullable JsonFormat.Printer printer, @Nullable ExtensionRegistry extensionRegistry) {
+
+		super(new ProtobufJavaUtilSupport(parser, printer), extensionRegistry);
 	}
 
 	/**
@@ -66,11 +83,17 @@ public class ProtobufJsonFormatHttpMessageConverter extends ProtobufHttpMessageC
 	 * @param parser the JSON parser configuration
 	 * @param printer the JSON printer configuration
 	 * @param registryInitializer an initializer for message extensions
+	 * @deprecated as of Spring Framework 5.1, use
+	 * {@link #ProtobufJsonFormatHttpMessageConverter(JsonFormat.Parser, JsonFormat.Printer, ExtensionRegistry)} instead
 	 */
+	@Deprecated
 	public ProtobufJsonFormatHttpMessageConverter(@Nullable JsonFormat.Parser parser,
 			@Nullable JsonFormat.Printer printer, @Nullable ExtensionRegistryInitializer registryInitializer) {
 
-		super(new ProtobufJavaUtilSupport(parser, printer), registryInitializer);
+		super(new ProtobufJavaUtilSupport(parser, printer), null);
+		if (registryInitializer != null) {
+			registryInitializer.initializeExtensionRegistry(this.extensionRegistry);
+		}
 	}
 
 }
diff --git a/spring-web/src/test/java/org/springframework/http/converter/protobuf/ProtobufHttpMessageConverterTests.java b/spring-web/src/test/java/org/springframework/http/converter/protobuf/ProtobufHttpMessageConverterTests.java
index 345cedc85c..5a9326eb43 100644
--- a/spring-web/src/test/java/org/springframework/http/converter/protobuf/ProtobufHttpMessageConverterTests.java
+++ b/spring-web/src/test/java/org/springframework/http/converter/protobuf/ProtobufHttpMessageConverterTests.java
@@ -19,6 +19,7 @@ package org.springframework.http.converter.protobuf;
 import java.io.IOException;
 import java.nio.charset.Charset;
 
+import com.google.protobuf.ExtensionRegistry;
 import com.google.protobuf.Message;
 import com.google.protobuf.util.JsonFormat;
 import org.junit.Before;
@@ -39,11 +40,15 @@ import static org.mockito.Mockito.*;
  * @author Alex Antonov
  * @author Juergen Hoeller
  * @author Andreas Ahlenstorf
+ * @author Sebastien Deleuze
  */
+@SuppressWarnings("deprecation")
 public class ProtobufHttpMessageConverterTests {
 
 	private ProtobufHttpMessageConverter converter;
 
+	private ExtensionRegistry extensionRegistry;
+
 	private ExtensionRegistryInitializer registryInitializer;
 
 	private Msg testMsg;
@@ -52,6 +57,7 @@ public class ProtobufHttpMessageConverterTests {
 	@Before
 	public void setup() {
 		this.registryInitializer = mock(ExtensionRegistryInitializer.class);
+		this.extensionRegistry = mock(ExtensionRegistry.class);
 		this.converter = new ProtobufHttpMessageConverter(this.registryInitializer);
 		this.testMsg = Msg.newBuilder().setFoo("Foo").setBlah(SecondMsg.newBuilder().setBlah(123).build()).build();
 	}
@@ -62,9 +68,16 @@ public class ProtobufHttpMessageConverterTests {
 		verify(this.registryInitializer, times(1)).initializeExtensionRegistry(any());
 	}
 
+	@Test
+	public void extensionRegistryInitializerNull() {
+		ProtobufHttpMessageConverter converter = new ProtobufHttpMessageConverter((ExtensionRegistryInitializer)null);
+		assertNotNull(converter.extensionRegistry);
+	}
+
 	@Test
 	public void extensionRegistryNull() {
-		new ProtobufHttpMessageConverter(null);
+		ProtobufHttpMessageConverter converter = new ProtobufHttpMessageConverter((ExtensionRegistry)null);
+		assertNotNull(converter.extensionRegistry);
 	}
 
 	@Test
@@ -128,7 +141,7 @@ public class ProtobufHttpMessageConverterTests {
 	public void writeJsonWithGoogleProtobuf() throws IOException {
 		this.converter = new ProtobufHttpMessageConverter(
 				new ProtobufHttpMessageConverter.ProtobufJavaUtilSupport(null, null),
-				this.registryInitializer);
+				this.extensionRegistry);
 		MockHttpOutputMessage outputMessage = new MockHttpOutputMessage();
 		MediaType contentType = MediaType.APPLICATION_JSON_UTF8;
 		this.converter.write(this.testMsg, contentType, outputMessage);
@@ -152,7 +165,7 @@ public class ProtobufHttpMessageConverterTests {
 	public void writeJsonWithJavaFormat() throws IOException {
 		this.converter = new ProtobufHttpMessageConverter(
 				new ProtobufHttpMessageConverter.ProtobufJavaFormatSupport(),
-				this.registryInitializer);
+				this.extensionRegistry);
 		MockHttpOutputMessage outputMessage = new MockHttpOutputMessage();
 		MediaType contentType = MediaType.APPLICATION_JSON_UTF8;
 		this.converter.write(this.testMsg, contentType, outputMessage);
diff --git a/spring-web/src/test/java/org/springframework/http/converter/protobuf/ProtobufJsonFormatHttpMessageConverterTests.java b/spring-web/src/test/java/org/springframework/http/converter/protobuf/ProtobufJsonFormatHttpMessageConverterTests.java
index 350e484ff3..1ba7eec478 100644
--- a/spring-web/src/test/java/org/springframework/http/converter/protobuf/ProtobufJsonFormatHttpMessageConverterTests.java
+++ b/spring-web/src/test/java/org/springframework/http/converter/protobuf/ProtobufJsonFormatHttpMessageConverterTests.java
@@ -18,6 +18,7 @@ package org.springframework.http.converter.protobuf;
 
 import java.io.IOException;
 
+import com.google.protobuf.ExtensionRegistry;
 import com.google.protobuf.Message;
 import com.google.protobuf.util.JsonFormat;
 import org.junit.Before;
@@ -36,11 +37,15 @@ import static org.mockito.Mockito.*;
  * Test suite for {@link ProtobufJsonFormatHttpMessageConverter}.
  *
  * @author Juergen Hoeller
+ * @author Sebastien Deleuze
  */
+@SuppressWarnings("deprecation")
 public class ProtobufJsonFormatHttpMessageConverterTests {
 
 	private ProtobufHttpMessageConverter converter;
 
+	private ExtensionRegistry extensionRegistry;
+
 	private ExtensionRegistryInitializer registryInitializer;
 
 	private Msg testMsg;
@@ -49,6 +54,7 @@ public class ProtobufJsonFormatHttpMessageConverterTests {
 	@Before
 	public void setup() {
 		this.registryInitializer = mock(ExtensionRegistryInitializer.class);
+		this.extensionRegistry = mock(ExtensionRegistry.class);
 		this.converter = new ProtobufJsonFormatHttpMessageConverter(
 				JsonFormat.parser(), JsonFormat.printer(), this.registryInitializer);
 		this.testMsg = Msg.newBuilder().setFoo("Foo").setBlah(SecondMsg.newBuilder().setBlah(123).build()).build();
@@ -61,8 +67,15 @@ public class ProtobufJsonFormatHttpMessageConverterTests {
 	}
 
 	@Test
-	public void extensionRegistryNull() {
-		new ProtobufHttpMessageConverter(null);
+	public void extensionRegistryInitializerNull() {
+		ProtobufHttpMessageConverter converter = new ProtobufHttpMessageConverter((ExtensionRegistryInitializer)null);
+		assertNotNull(converter);
+	}
+
+	@Test
+	public void extensionRegistryInitializer() {
+		ProtobufHttpMessageConverter converter = new ProtobufHttpMessageConverter((ExtensionRegistry)null);
+		assertNotNull(converter);
 	}
 
 	@Test