diff --git a/README.md b/README.md
index e555373..5dbc7c8 100644
--- a/README.md
+++ b/README.md
@@ -72,7 +72,7 @@ The primary goals of this framework are:
 - [x] Support ability to distinguish between `Attributes` fields that are optional (i.e. the key might not be there) and `Attributes` values that are optional (i.e. the key is guaranteed to be there but it might be `null`).
 - [x] Fix `ToOneRelationship` so that it is possible to specify an optional relationship where the value is `null` rather than the key being omitted.
 - [x] Conform to `CustomStringConvertible`
-- [ ] More tests around failing to decode improperly structured JSON (not bad JSON, but JSON that is not to spec)
+- [x] More tests around failing to decode improperly structured JSON (not bad JSON, but JSON that is not to spec)
 - [ ] Use `KeyPath` to specify `Includes` thus creating type safety around the relationship between a primary resource type and the types of included resources????
 - [x] For `NoIncludes`, do not even loop over the "included" JSON API section if it exists.
 - [ ] Property-based testing (using `SwiftCheck`)
diff --git a/Tests/JSONAPITests/Relationships/RelationshipTests.swift b/Tests/JSONAPITests/Relationships/RelationshipTests.swift
index 3460e51..459dd3b 100644
--- a/Tests/JSONAPITests/Relationships/RelationshipTests.swift
+++ b/Tests/JSONAPITests/Relationships/RelationshipTests.swift
@@ -61,6 +61,17 @@ extension RelationshipTests {
 	}
 }
 
+// MARK: Failure tests
+extension RelationshipTests {
+	func test_ToManyTypeMismatch() {
+		XCTAssertThrowsError(try JSONDecoder().decode(ToManyRelationship<TestEntity1>.self, from: to_many_relationship_type_mismatch))
+	}
+
+	func test_ToOneTypeMismatch() {
+		XCTAssertThrowsError(try JSONDecoder().decode(ToOneRelationship<TestEntity1>.self, from: to_one_relationship_type_mismatch))
+	}
+}
+
 // MARK: - Test types
 extension RelationshipTests {
 	enum TestEntityType1: EntityDescription {
diff --git a/Tests/JSONAPITests/Relationships/stubs/RelationshipStubs.swift b/Tests/JSONAPITests/Relationships/stubs/RelationshipStubs.swift
index e2508ad..6be0d90 100644
--- a/Tests/JSONAPITests/Relationships/stubs/RelationshipStubs.swift
+++ b/Tests/JSONAPITests/Relationships/stubs/RelationshipStubs.swift
@@ -14,6 +14,15 @@ let to_one_relationship = """
 }
 """.data(using: .utf8)!
 
+let to_one_relationship_type_mismatch = """
+{
+	"data": {
+		"type": "not_a_type",
+		"id": "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"
+	}
+}
+""".data(using: .utf8)!
+
 let to_many_relationship = """
 {
 	"data": [
@@ -32,3 +41,22 @@ let to_many_relationship = """
 	]
 }
 """.data(using: .utf8)!
+
+let to_many_relationship_type_mismatch = """
+{
+	"data": [
+		{
+			"type": "test_entity1",
+			"id": "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"
+		},
+		{
+			"type": "test_entity1",
+			"id": "90F03B69-4DF1-467F-B52E-B0C9E44FC333"
+		},
+		{
+			"type": "not_a_type",
+			"id": "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"
+		}
+	]
+}
+""".data(using: .utf8)!