diff --git a/spring-graphql-web/src/main/java/org/springframework/graphql/RequestInput.java b/spring-graphql-web/src/main/java/org/springframework/graphql/RequestInput.java
index d46dd0a8..99c77093 100644
--- a/spring-graphql-web/src/main/java/org/springframework/graphql/RequestInput.java
+++ b/spring-graphql-web/src/main/java/org/springframework/graphql/RequestInput.java
@@ -4,6 +4,8 @@ import java.util.Collections;
 import java.util.Map;
 
 import org.springframework.lang.Nullable;
+import org.springframework.util.StringUtils;
+import org.springframework.web.server.ServerWebInputException;
 
 /**
  * @author Andreas Marek
@@ -50,4 +52,10 @@ class RequestInput {
 	public void setVariables(Map<String, Object> variables) {
 		this.variables = variables;
 	}
+
+	public void validate() {
+		if (!StringUtils.hasText(getQuery())) {
+			throw new ServerWebInputException("Missing query");
+		}
+	}
 }
diff --git a/spring-graphql-web/src/main/java/org/springframework/graphql/WebFluxGraphQLHandler.java b/spring-graphql-web/src/main/java/org/springframework/graphql/WebFluxGraphQLHandler.java
index 20f8d724..a9c574f8 100644
--- a/spring-graphql-web/src/main/java/org/springframework/graphql/WebFluxGraphQLHandler.java
+++ b/spring-graphql-web/src/main/java/org/springframework/graphql/WebFluxGraphQLHandler.java
@@ -6,10 +6,15 @@ import graphql.GraphQL;
 import reactor.core.publisher.Mono;
 
 import org.springframework.http.HttpHeaders;
+import org.springframework.web.reactive.function.server.HandlerFunction;
 import org.springframework.web.reactive.function.server.ServerRequest;
 import org.springframework.web.reactive.function.server.ServerResponse;
 
-public class WebFluxGraphQLHandler {
+/**
+ * GraphQL handler to be exposed as a WebFlux.fn endpoint via
+ * {@link org.springframework.web.reactive.function.server.RouterFunctions}.
+ */
+public class WebFluxGraphQLHandler implements HandlerFunction<ServerResponse> {
 
 	private final GraphQL graphQL;
 
@@ -19,15 +24,12 @@ public class WebFluxGraphQLHandler {
 
 	public Mono<ServerResponse> handle(ServerRequest request) {
 		return request.bodyToMono(RequestInput.class)
-				.flatMap(body -> {
-					String query = body.getQuery();
-					if (query == null) {
-						query = "";
-					}
+				.flatMap(requestInput -> {
+					requestInput.validate();
 					ExecutionInput executionInput = ExecutionInput.newExecutionInput()
-							.query(query)
-							.operationName(body.getOperationName())
-							.variables(body.getVariables())
+							.query(requestInput.getQuery())
+							.operationName(requestInput.getOperationName())
+							.variables(requestInput.getVariables())
 							.build();
 					// Invoke GraphQLInterceptor's preHandle here
 					return customizeExecutionInput(executionInput, request.headers().asHttpHeaders());
diff --git a/spring-graphql-web/src/main/java/org/springframework/graphql/WebMvcGraphQLHandler.java b/spring-graphql-web/src/main/java/org/springframework/graphql/WebMvcGraphQLHandler.java
index 71af3b0f..439481b5 100644
--- a/spring-graphql-web/src/main/java/org/springframework/graphql/WebMvcGraphQLHandler.java
+++ b/spring-graphql-web/src/main/java/org/springframework/graphql/WebMvcGraphQLHandler.java
@@ -12,12 +12,18 @@ import graphql.ExecutionResult;
 import graphql.GraphQL;
 
 import org.springframework.http.HttpHeaders;
+import org.springframework.web.HttpMediaTypeNotSupportedException;
 import org.springframework.web.server.ServerErrorException;
 import org.springframework.web.server.ServerWebInputException;
+import org.springframework.web.servlet.function.HandlerFunction;
 import org.springframework.web.servlet.function.ServerRequest;
 import org.springframework.web.servlet.function.ServerResponse;
 
-public class WebMvcGraphQLHandler {
+/**
+ * GraphQL handler to be exposed as a WebMvc.fn endpoint via
+ * {@link org.springframework.web.servlet.function.RouterFunctions}.
+ */
+public class WebMvcGraphQLHandler implements HandlerFunction<ServerResponse> {
 
 	private final GraphQL graphQL;
 
@@ -25,36 +31,38 @@ public class WebMvcGraphQLHandler {
 		this.graphQL = graphQL.build();
 	}
 
-	public ServerResponse handle(ServerRequest serverRequest) {
-		RequestInput body;
+	/**
+	 * {@inheritDoc}
+	 *
+	 * @throws ServletException may be raised when reading the request body,
+	 * e.g. {@link HttpMediaTypeNotSupportedException}.
+	 */
+	public ServerResponse handle(ServerRequest request) throws ServletException {
+		RequestInput requestInput;
 		try {
-			body = serverRequest.body(RequestInput.class);
+			requestInput = request.body(RequestInput.class);
+			requestInput.validate();
 		}
-		catch (ServletException | IOException ex) {
-			throw new ServerWebInputException("Failed to read request body", null, ex);
+		catch (IOException ex) {
+			throw new ServerWebInputException("I/O error while reading request body", null, ex);
 		}
-		String query = body.getQuery();
-		if (query == null) {
-			query = "";
-		}
-		ExecutionInput input = ExecutionInput.newExecutionInput()
-				.query(query)
-				.operationName(body.getOperationName())
-				.variables(body.getVariables())
+
+		ExecutionInput executionInput = ExecutionInput.newExecutionInput()
+				.query(requestInput.getQuery())
+				.operationName(requestInput.getOperationName())
+				.variables(requestInput.getVariables())
 				.build();
 
 		// Invoke GraphQLInterceptor's preHandle here
 
 		CompletableFuture<Map<String, Object>> future =
-				customizeExecutionInput(input, serverRequest.headers().asHttpHeaders())
+				customizeExecutionInput(executionInput, request.headers().asHttpHeaders())
 						.thenCompose(this::execute)
 						.thenApply(ExecutionResult::toSpecification);
 
 		// Invoke GraphQLInterceptor's postHandle here
 
-		return future.isDone() ?
-				ServerResponse.ok().body(getResult(future)) :
-				ServerResponse.ok().body(future);
+		return ServerResponse.ok().body(future.isDone() ? getResult(future) : future);
 	}
 
 	protected CompletableFuture<ExecutionInput> customizeExecutionInput(ExecutionInput input, HttpHeaders headers) {