diff --git a/spring-messaging/src/main/java/org/springframework/messaging/rsocket/DefaultRSocketRequesterBuilder.java b/spring-messaging/src/main/java/org/springframework/messaging/rsocket/DefaultRSocketRequesterBuilder.java
index 247f66abee..197d77f967 100644
--- a/spring-messaging/src/main/java/org/springframework/messaging/rsocket/DefaultRSocketRequesterBuilder.java
+++ b/spring-messaging/src/main/java/org/springframework/messaging/rsocket/DefaultRSocketRequesterBuilder.java
@@ -145,21 +145,14 @@ final class DefaultRSocketRequesterBuilder implements RSocketRequester.Builder {
 		if (this.dataMimeType != null) {
 			return this.dataMimeType;
 		}
-		// Look for non-basic Decoder (e.g. CBOR, Protobuf)
-		MimeType selected = null;
-		List<Decoder<?>> decoders = strategies.decoders();
-		for (Decoder<?> candidate : decoders) {
+		// First non-basic Decoder (e.g. CBOR, Protobuf)
+		for (Decoder<?> candidate : strategies.decoders()) {
 			if (!isCoreCodec(candidate) && !candidate.getDecodableMimeTypes().isEmpty()) {
-				Assert.state(selected == null,
-						() -> "Cannot select default data MimeType based on configured decoders: " + decoders);
-				selected = getMimeType(candidate);
+				return getMimeType(candidate);
 			}
 		}
-		if (selected != null) {
-			return selected;
-		}
-		// Fall back on 1st decoder (e.g. String)
-		for (Decoder<?> decoder : decoders) {
+		// First core decoder (e.g. String)
+		for (Decoder<?> decoder : strategies.decoders()) {
 			if (!decoder.getDecodableMimeTypes().isEmpty()) {
 				return getMimeType(decoder);
 			}
diff --git a/spring-messaging/src/main/java/org/springframework/messaging/rsocket/RSocketRequester.java b/spring-messaging/src/main/java/org/springframework/messaging/rsocket/RSocketRequester.java
index ef9643632f..a1b834f6b3 100644
--- a/spring-messaging/src/main/java/org/springframework/messaging/rsocket/RSocketRequester.java
+++ b/spring-messaging/src/main/java/org/springframework/messaging/rsocket/RSocketRequester.java
@@ -128,11 +128,10 @@ public interface RSocketRequester {
 		/**
 		 * Configure the payload data MimeType to specify on the {@code SETUP}
 		 * frame that applies to the whole connection.
-		 * <p>If this is not set, the builder will try to select the mime type
-		 * based on the presence of a single
+		 * <p>If this is not set, it will be set to the MimeType of the first
 		 * {@link RSocketStrategies.Builder#decoder(Decoder[])  non-default}
-		 * {@code Decoder}, or the first default decoder otherwise
-		 * (i.e. {@code String}) if no others are configured.
+		 * {@code Decoder}, or otherwise fall back on the MimeType of the first
+		 * (default) decoder.
 		 */
 		RSocketRequester.Builder dataMimeType(@Nullable MimeType mimeType);
 
diff --git a/spring-messaging/src/main/java/org/springframework/messaging/rsocket/annotation/support/RSocketMessageHandler.java b/spring-messaging/src/main/java/org/springframework/messaging/rsocket/annotation/support/RSocketMessageHandler.java
index a66bf95379..52392bdb28 100644
--- a/spring-messaging/src/main/java/org/springframework/messaging/rsocket/annotation/support/RSocketMessageHandler.java
+++ b/spring-messaging/src/main/java/org/springframework/messaging/rsocket/annotation/support/RSocketMessageHandler.java
@@ -304,7 +304,13 @@ public class RSocketMessageHandler extends MessageMappingMessageHandler {
 	 */
 	public SocketAcceptor serverResponder() {
 		return (setupPayload, sendingRSocket) -> {
-			MessagingRSocket responder = createResponder(setupPayload, sendingRSocket);
+			MessagingRSocket responder;
+			try {
+				responder = createResponder(setupPayload, sendingRSocket);
+			}
+			catch (Throwable ex) {
+				return Mono.error(ex);
+			}
 			return responder.handleConnectionSetupPayload(setupPayload).then(Mono.just(responder));
 		};
 	}
@@ -335,14 +341,15 @@ public class RSocketMessageHandler extends MessageMappingMessageHandler {
 		String s = setupPayload.dataMimeType();
 		MimeType dataMimeType = StringUtils.hasText(s) ? MimeTypeUtils.parseMimeType(s) : this.defaultDataMimeType;
 		Assert.notNull(dataMimeType, "No `dataMimeType` in ConnectionSetupPayload and no default value");
+		Assert.isTrue(isDataMimeTypeSupported(dataMimeType), "Data MimeType '" + dataMimeType + "' not supported");
 
 		s = setupPayload.metadataMimeType();
-		MimeType metadataMimeType = StringUtils.hasText(s) ? MimeTypeUtils.parseMimeType(s) : this.defaultMetadataMimeType;
-		Assert.notNull(metadataMimeType, "No `metadataMimeType` in ConnectionSetupPayload and no default value");
+		MimeType metaMimeType = StringUtils.hasText(s) ? MimeTypeUtils.parseMimeType(s) : this.defaultMetadataMimeType;
+		Assert.notNull(metaMimeType, "No `metadataMimeType` in ConnectionSetupPayload and no default value");
 
 		RSocketStrategies strategies = this.rsocketStrategies;
 		Assert.notNull(strategies, "No RSocketStrategies. Was afterPropertiesSet not called?");
-		RSocketRequester requester = RSocketRequester.wrap(rsocket, dataMimeType, metadataMimeType, strategies);
+		RSocketRequester requester = RSocketRequester.wrap(rsocket, dataMimeType, metaMimeType, strategies);
 
 		Assert.state(this.metadataExtractor != null,
 				() -> "No MetadataExtractor. Was afterPropertiesSet not called?");
@@ -350,10 +357,20 @@ public class RSocketMessageHandler extends MessageMappingMessageHandler {
 		Assert.state(getRouteMatcher() != null,
 				() -> "No RouteMatcher. Was afterPropertiesSet not called?");
 
-		return new MessagingRSocket(dataMimeType, metadataMimeType, this.metadataExtractor, requester,
+		return new MessagingRSocket(dataMimeType, metaMimeType, this.metadataExtractor, requester,
 				this, getRouteMatcher(), strategies);
 	}
 
+	private boolean isDataMimeTypeSupported(MimeType dataMimeType) {
+		for (Encoder<?> encoder : getEncoders()) {
+			for (MimeType encodable : encoder.getEncodableMimeTypes()) {
+				if (encodable.isCompatibleWith(dataMimeType)) {
+					return true;
+				}
+			}
+		}
+		return false;
+	}
 
 	public static ClientRSocketFactoryConfigurer clientResponder(Object... handlers) {
 		return new ResponderConfigurer(handlers);
diff --git a/spring-messaging/src/test/java/org/springframework/messaging/rsocket/DefaultRSocketRequesterBuilderTests.java b/spring-messaging/src/test/java/org/springframework/messaging/rsocket/DefaultRSocketRequesterBuilderTests.java
index bd497b5860..d0ed124cd5 100644
--- a/spring-messaging/src/test/java/org/springframework/messaging/rsocket/DefaultRSocketRequesterBuilderTests.java
+++ b/spring-messaging/src/test/java/org/springframework/messaging/rsocket/DefaultRSocketRequesterBuilderTests.java
@@ -46,7 +46,6 @@ import org.springframework.util.MimeTypeUtils;
 import org.springframework.util.ReflectionUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
-import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyInt;
 import static org.mockito.BDDMockito.given;
@@ -131,22 +130,6 @@ public class DefaultRSocketRequesterBuilderTests {
 				.isEqualTo(MimeTypeUtils.APPLICATION_JSON);
 	}
 
-	@Test
-	public void defaultDataMimeTypeWithMultipleCustomDecoderRegitered() {
-		RSocketStrategies strategies = RSocketStrategies.builder()
-				.decoder(new TestJsonDecoder(MimeTypeUtils.APPLICATION_JSON))
-				.decoder(new TestJsonDecoder(MimeTypeUtils.APPLICATION_XML))
-				.build();
-
-		assertThatThrownBy(() ->
-				RSocketRequester
-						.builder()
-						.rsocketStrategies(strategies)
-						.connect(this.transport)
-						.block())
-				.hasMessageContaining("Cannot select default data MimeType");
-	}
-
 	@Test
 	public void dataMimeTypeSet() {
 		RSocketRequester requester = RSocketRequester.builder()