diff --git a/Sources/JSONAPI/Error/BasicJSONAPIError.swift b/Sources/JSONAPI/Error/BasicJSONAPIError.swift
index 345af26..fa0158d 100644
--- a/Sources/JSONAPI/Error/BasicJSONAPIError.swift
+++ b/Sources/JSONAPI/Error/BasicJSONAPIError.swift
@@ -70,4 +70,9 @@ public struct BasicJSONAPIErrorPayload<IdType: Codable & Equatable>: Codable, Eq
 /// a good option if you do not know what to expect. You could also use
 /// `Either<Int, String>` (provided by the `Poly` package that is
 /// already a dependency of `JSONAPI`).
+///
+///  - Important: The `definedFields` property will include fields
+///     with non-nil values in a flattened way. There will be no `source` key
+///     but there will be `pointer` and `parameter` keys (if those values
+///     are non-nil).
 public typealias BasicJSONAPIError<IdType: Codable & Equatable> = GenericJSONAPIError<BasicJSONAPIErrorPayload<IdType>>
diff --git a/Tests/JSONAPITests/Error/BasicJSONAPIErrorTests.swift b/Tests/JSONAPITests/Error/BasicJSONAPIErrorTests.swift
new file mode 100644
index 0000000..e726143
--- /dev/null
+++ b/Tests/JSONAPITests/Error/BasicJSONAPIErrorTests.swift
@@ -0,0 +1,92 @@
+//
+//  BasicJSONAPIErrorTests.swift
+//  JSONAPITests
+//
+//  Created by Mathew Polzin on 9/29/19.
+//
+
+import Foundation
+@testable import JSONAPI
+import XCTest
+
+final class BasicJSONAPIErrorTests: XCTestCase {
+    func test_initAndEquality() {
+        let unknown1 = BasicJSONAPIError<String>.unknown
+        let unknown2 = BasicJSONAPIError<String>.unknownError
+        XCTAssertEqual(unknown1, unknown2)
+        let unknown3 = BasicJSONAPIError<Int>.unknownError
+        XCTAssertEqual(unknown3, .unknown)
+
+        let _ = BasicJSONAPIError<Int>.error(.init(id: nil,
+                                                   status: nil,
+                                                   code: nil,
+                                                   title: nil,
+                                                   detail: nil,
+                                                   source: nil))
+        let _ = BasicJSONAPIError<String>.error(.init(id: nil,
+                                                      status: nil,
+                                                      code: nil,
+                                                      title: nil,
+                                                      detail: nil,
+                                                      source: nil))
+
+        let intError = BasicJSONAPIError<Int>.error(.init(id: 2,
+                                                          status: nil,
+                                                          code: nil,
+                                                          title: nil,
+                                                          detail: nil,
+                                                          source: nil))
+        XCTAssertEqual(intError.payload?.id, 2)
+        XCTAssertNotEqual(intError, unknown3)
+
+        let stringError = BasicJSONAPIError<String>.error(.init(id: "hello",
+                                                                status: nil,
+                                                                code: nil,
+                                                                title: nil,
+                                                                detail: nil,
+                                                                source: nil))
+        XCTAssertEqual(stringError.payload?.id, "hello")
+        XCTAssertNotEqual(stringError, unknown1)
+
+        let wellPopulatedError = BasicJSONAPIError<Int>.error(.init(id: 10,
+                                                                    status: "404",
+                                                                    code: "12",
+                                                                    title: "Missing",
+                                                                    detail: "Resource was not found",
+                                                                    source: .init(pointer: "/data/attributes/id", parameter: "id")))
+        XCTAssertEqual(wellPopulatedError.payload?.id, 10)
+        XCTAssertEqual(wellPopulatedError.payload?.status, "404")
+        XCTAssertEqual(wellPopulatedError.payload?.code, "12")
+        XCTAssertEqual(wellPopulatedError.payload?.title, "Missing")
+        XCTAssertEqual(wellPopulatedError.payload?.detail, "Resource was not found")
+        XCTAssertEqual(wellPopulatedError.payload?.source?.pointer, "/data/attributes/id")
+        XCTAssertEqual(wellPopulatedError.payload?.source?.parameter, "id")
+
+        XCTAssertNotEqual(wellPopulatedError, intError)
+    }
+
+    func test_definedFields() {
+        let unpopulatedError = BasicJSONAPIError<Int>.error(.init(id: nil,
+                                                                  status: nil,
+                                                                  code: nil,
+                                                                  title: nil,
+                                                                  detail: nil,
+                                                                  source: nil))
+        XCTAssertEqual(unpopulatedError.definedFields.count, 0)
+
+        let wellPopulatedError = BasicJSONAPIError<Int>.error(.init(id: 10,
+                                                                    status: "404",
+                                                                    code: "12",
+                                                                    title: "Missing",
+                                                                    detail: "Resource was not found",
+                                                                    source: .init(pointer: "/data/attributes/id", parameter: "id")))
+        XCTAssertEqual(wellPopulatedError.definedFields.count, 7)
+        XCTAssertEqual(wellPopulatedError.definedFields["id"], "10")
+        XCTAssertEqual(wellPopulatedError.definedFields["status"], "404")
+        XCTAssertEqual(wellPopulatedError.definedFields["code"], "12")
+        XCTAssertEqual(wellPopulatedError.definedFields["title"], "Missing")
+        XCTAssertEqual(wellPopulatedError.definedFields["detail"], "Resource was not found")
+        XCTAssertEqual(wellPopulatedError.definedFields["pointer"], "/data/attributes/id")
+        XCTAssertEqual(wellPopulatedError.definedFields["parameter"], "id")
+    }
+}
diff --git a/Tests/JSONAPITests/Error/GenericJSONAPIErrorTests.swift b/Tests/JSONAPITests/Error/GenericJSONAPIErrorTests.swift
index e1fca6e..21172ed 100644
--- a/Tests/JSONAPITests/Error/GenericJSONAPIErrorTests.swift
+++ b/Tests/JSONAPITests/Error/GenericJSONAPIErrorTests.swift
@@ -92,6 +92,14 @@ final class GenericJSONAPIErrorTests: XCTestCase {
         }
     }
 
+    func test_encodeUnknown() {
+        let error = TestGenericJSONAPIError.unknownError
+
+        let encodedError = encoded(value: ["errors": [error]])
+
+        XCTAssertEqual(String(data: encodedError, encoding: .utf8)!, #"{"errors":["unknown"]}"#)
+    }
+
     func test_payloadAccess() {
         let error1 = TestGenericJSONAPIError.error(.init(hello: "world", world: 3))
         let error2 = TestGenericJSONAPIError.error(.init(hello: "there", world: nil))