diff --git a/spring-graphql/src/main/java/org/springframework/graphql/data/GraphQlArgumentBinder.java b/spring-graphql/src/main/java/org/springframework/graphql/data/GraphQlArgumentBinder.java
index 7388491e..11508ec3 100644
--- a/spring-graphql/src/main/java/org/springframework/graphql/data/GraphQlArgumentBinder.java
+++ b/spring-graphql/src/main/java/org/springframework/graphql/data/GraphQlArgumentBinder.java
@@ -128,7 +128,7 @@ public class GraphQlArgumentBinder {
 		try {
 			// From Collection
 
-			if (CollectionFactory.isApproximableCollectionType(rawValue.getClass())) {
+			if (isApproximableCollectionType(rawValue)) {
 				segments.push(argumentName);
 				return createCollection((Collection<Object>) rawValue, targetType, bindingResult, segments);
 			}
@@ -164,6 +164,11 @@ public class GraphQlArgumentBinder {
 		return (type.resolve(Object.class).equals(Optional.class) ? Optional.ofNullable(value) : value);
 	}
 
+	private boolean isApproximableCollectionType(Object rawValue) {
+		return (CollectionFactory.isApproximableCollectionType(rawValue.getClass()) ||
+				rawValue instanceof List);  // it may be SingletonList
+	}
+
 	@SuppressWarnings({"ConstantConditions", "unchecked"})
 	private <T> Collection<T> createCollection(
 			Collection<Object> rawCollection, ResolvableType collectionType,
@@ -253,7 +258,7 @@ public class GraphQlArgumentBinder {
 			if (rawValue == null && methodParam.isOptional()) {
 				args[i] = (paramTypes[i] == Optional.class ? Optional.empty() : null);
 			}
-			else if (rawValue != null && CollectionFactory.isApproximableCollectionType(rawValue.getClass())) {
+			else if (rawValue != null && isApproximableCollectionType(rawValue)) {
 				ResolvableType elementType = ResolvableType.forMethodParameter(methodParam);
 				args[i] = createCollection((Collection<Object>) rawValue, elementType, bindingResult, segments);
 			}
diff --git a/spring-graphql/src/test/java/org/springframework/graphql/data/method/annotation/support/GraphQlArgumentBinderTests.java b/spring-graphql/src/test/java/org/springframework/graphql/data/GraphQlArgumentBinderTests.java
similarity index 87%
rename from spring-graphql/src/test/java/org/springframework/graphql/data/method/annotation/support/GraphQlArgumentBinderTests.java
rename to spring-graphql/src/test/java/org/springframework/graphql/data/GraphQlArgumentBinderTests.java
index 00f9cb63..89949929 100644
--- a/spring-graphql/src/test/java/org/springframework/graphql/data/method/annotation/support/GraphQlArgumentBinderTests.java
+++ b/spring-graphql/src/test/java/org/springframework/graphql/data/GraphQlArgumentBinderTests.java
@@ -14,8 +14,10 @@
  * limitations under the License.
  */
 
-package org.springframework.graphql.data.method.annotation.support;
+package org.springframework.graphql.data;
 
+import java.util.Collections;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
@@ -45,14 +47,13 @@ class GraphQlArgumentBinderTests {
 
 	private final ObjectMapper mapper = new ObjectMapper();
 
-	private final ThreadLocal<GraphQlArgumentBinder> initializer =
-			ThreadLocal.withInitial(() -> new GraphQlArgumentBinder(null));
+	private final GraphQlArgumentBinder binder = new GraphQlArgumentBinder(null);
 
 
 	@Test
 	void defaultConstructor() throws Exception {
 
-		Object result = initializer.get().bind(
+		Object result = this.binder.bind(
 				environment("{\"key\":{\"name\":\"test\"}}"), "key",
 				ResolvableType.forClass(SimpleBean.class));
 
@@ -63,7 +64,7 @@ class GraphQlArgumentBinderTests {
 	@Test
 	void defaultConstructorWithNestedBeanProperty() throws Exception {
 
-		Object result = initializer.get().bind(
+		Object result = this.binder.bind(
 				environment(
 						"{\"key\":{" +
 								"\"name\":\"test name\"," +
@@ -84,7 +85,7 @@ class GraphQlArgumentBinderTests {
 	@Test
 	void defaultConstructorWithNestedBeanListProperty() throws Exception {
 
-		Object result = initializer.get().bind(
+		Object result = this.binder.bind(
 				environment("{\"key\":{\"items\":[{\"name\":\"first\"},{\"name\":\"second\"}]}}"), "key",
 				ResolvableType.forClass(ItemListHolder.class));
 
@@ -96,7 +97,7 @@ class GraphQlArgumentBinderTests {
 	@Test // gh-301
 	void defaultConstructorWithNestedBeanListEmpty() throws Exception {
 
-		Object result = initializer.get().bind(
+		Object result = this.binder.bind(
 				environment("{\"key\":{\"items\": []}}"), "key",
 				ResolvableType.forClass(ItemListHolder.class));
 
@@ -108,7 +109,7 @@ class GraphQlArgumentBinderTests {
 	void defaultConstructorBindingError() {
 
 		assertThatThrownBy(
-				() -> initializer.get().bind(
+				() -> this.binder.bind(
 						environment("{\"key\":{\"name\":\"test\",\"age\":\"invalid\"}}"), "key",
 						ResolvableType.forClass(SimpleBean.class)))
 				.extracting(ex -> ((BindException) ex).getFieldErrors())
@@ -123,7 +124,7 @@ class GraphQlArgumentBinderTests {
 	@Test
 	void primaryConstructor() throws Exception {
 
-		Object result = initializer.get().bind(
+		Object result = this.binder.bind(
 				environment("{\"key\":{\"name\":\"test\"}}"), "key",
 				ResolvableType.forClass(PrimaryConstructorBean.class));
 
@@ -134,7 +135,7 @@ class GraphQlArgumentBinderTests {
 	@Test
 	void primaryConstructorWithBeanArgument() throws Exception {
 
-		Object result = initializer.get().bind(
+		Object result = this.binder.bind(
 				environment(
 						"{\"key\":{" +
 								"\"item\":{\"name\":\"Item name\"}," +
@@ -152,7 +153,7 @@ class GraphQlArgumentBinderTests {
 	@Test
 	void primaryConstructorWithNestedBeanList() throws Exception {
 
-		Object result = initializer.get().bind(
+		Object result = this.binder.bind(
 				environment(
 						"{\"key\":{\"items\":[" +
 								"{\"name\":\"first\"}," +
@@ -168,7 +169,7 @@ class GraphQlArgumentBinderTests {
 	@Test
 	void primaryConstructorNotFound() {
 		assertThatThrownBy(
-				() -> initializer.get().bind(
+				() -> this.binder.bind(
 						environment("{\"key\":{\"name\":\"test\"}}"), "key",
 						ResolvableType.forClass(NoPrimaryConstructorBean.class)))
 				.isInstanceOf(IllegalStateException.class)
@@ -179,7 +180,7 @@ class GraphQlArgumentBinderTests {
 	void primaryConstructorBindingError() {
 
 		assertThatThrownBy(
-				() -> initializer.get().bind(
+				() -> this.binder.bind(
 						environment(
 								"{\"key\":{" +
 										"\"name\":\"Hello\"," +
@@ -205,7 +206,7 @@ class GraphQlArgumentBinderTests {
 	void primaryConstructorBindingErrorWithNestedBeanList() {
 
 		assertThatThrownBy(
-				() -> initializer.get().bind(
+				() -> this.binder.bind(
 						environment(
 								"{\"key\":{\"items\":[" +
 										"{\"name\":\"first\", \"age\":\"invalid\"}," +
@@ -225,6 +226,31 @@ class GraphQlArgumentBinderTests {
 				});
 	}
 
+	@Test // gh-410
+	void coercionWithSingletonList() throws Exception {
+
+		Map<String, String> itemMap = new HashMap<>();
+		itemMap.put("name", "Joe");
+		itemMap.put("age", "37");
+
+		Map<String, Object> arguments = new HashMap<>();
+		arguments.put("key", Collections.singletonList(itemMap));
+
+		DataFetchingEnvironment environment =
+				DataFetchingEnvironmentImpl.newDataFetchingEnvironment().arguments(arguments).build();
+
+		Object result = this.binder.bind(environment, "key",
+				ResolvableType.forClassWithGenerics(List.class, Item.class));
+
+		assertThat(result).isNotNull().isInstanceOf(List.class);
+		List<Item> items = (List<Item>) result;
+
+		assertThat(items).hasSize(1);
+		assertThat(items.get(0).getName()).isEqualTo("Joe");
+		assertThat(items.get(0).getAge()).isEqualTo(37);
+	}
+
+
 	@SuppressWarnings("unchecked")
 	private DataFetchingEnvironment environment(String jsonPayload) throws JsonProcessingException {
 		Map<String, Object> arguments = this.mapper.readValue(jsonPayload, Map.class);