diff --git a/Sources/ApolloCodegenLib/ApolloCodegenConfiguration.swift b/Sources/ApolloCodegenLib/ApolloCodegenConfiguration.swift
index 2f12392ee..5272077c7 100644
--- a/Sources/ApolloCodegenLib/ApolloCodegenConfiguration.swift
+++ b/Sources/ApolloCodegenLib/ApolloCodegenConfiguration.swift
@@ -202,7 +202,7 @@ public struct ApolloCodegenConfiguration: Codable, Equatable {
 
     // MARK: Codable
 
-    enum CodingKeys: CodingKey {
+    enum CodingKeys: CodingKey, CaseIterable {
       case schemaTypes
       case operations
       case testMocks
@@ -214,7 +214,7 @@ public struct ApolloCodegenConfiguration: Codable, Equatable {
     /// specified defaults when not present.
     public init(from decoder: Decoder) throws {
       let values = try decoder.container(keyedBy: CodingKeys.self)
-
+      try throwIfContainsUnexpectedKey(container: values, type: Self.self, decoder: decoder)
       schemaTypes = try values.decode(
         SchemaTypesFileOutput.self,
         forKey: .schemaTypes
@@ -617,7 +617,7 @@ public struct ApolloCodegenConfiguration: Codable, Equatable {
 
     // MARK: Codable
 
-    enum CodingKeys: CodingKey {
+    enum CodingKeys: CodingKey, CaseIterable {
       case additionalInflectionRules
       case queryStringLiteralFormat
       case deprecatedEnumCases
@@ -633,6 +633,7 @@ public struct ApolloCodegenConfiguration: Codable, Equatable {
 
     public init(from decoder: Decoder) throws {
       let values = try decoder.container(keyedBy: CodingKeys.self)
+      try throwIfContainsUnexpectedKey(container: values, type: Self.self, decoder: decoder)
 
       additionalInflectionRules = try values.decodeIfPresent(
         [InflectionRule].self,
@@ -757,6 +758,13 @@ public struct ApolloCodegenConfiguration: Codable, Equatable {
 
     public init(from decoder: Decoder) throws {
       let values = try decoder.container(keyedBy: CodingKeys.self)
+      guard values.allKeys.first != nil else {
+        throw DecodingError.typeMismatch(Self.self, DecodingError.Context.init(
+          codingPath: values.codingPath,
+          debugDescription: "Invalid number of keys found, expected one.",
+          underlyingError: nil
+        ))
+      }
 
       enumCases = try values.decodeIfPresent(
         CaseConversionStrategy.self,
@@ -931,7 +939,7 @@ public struct ApolloCodegenConfiguration: Codable, Equatable {
 
     // MARK: Codable
 
-    public enum CodingKeys: CodingKey {
+    public enum CodingKeys: CodingKey, CaseIterable {
       case clientControlledNullability
       case legacySafelistingCompatibleOperations
     }
@@ -1008,7 +1016,7 @@ public struct ApolloCodegenConfiguration: Codable, Equatable {
 
   // MARK: Codable
 
-  enum CodingKeys: CodingKey {
+  enum CodingKeys: CodingKey, CaseIterable {
     case schemaName
     case schemaNamespace
     case input
@@ -1034,6 +1042,7 @@ public struct ApolloCodegenConfiguration: Codable, Equatable {
 
   public init(from decoder: Decoder) throws {
     let values = try decoder.container(keyedBy: CodingKeys.self)
+    try throwIfContainsUnexpectedKey(container: values, type: Self.self, decoder: decoder)
 
     func getSchemaNamespaceValue() throws -> String {
       if let value = try values.decodeIfPresent(String.self, forKey: .schemaNamespace) {
@@ -1152,7 +1161,7 @@ extension ApolloCodegenConfiguration.SelectionSetInitializers {
 
   // MARK: Codable
 
-  enum CodingKeys: CodingKey {
+  enum CodingKeys: CodingKey, CaseIterable {
     case operations
     case namedFragments
     case localCacheMutations
@@ -1161,6 +1170,7 @@ extension ApolloCodegenConfiguration.SelectionSetInitializers {
 
   public init(from decoder: Decoder) throws {
     let values = try decoder.container(keyedBy: CodingKeys.self)
+    try throwIfContainsUnexpectedKey(container: values, type: Self.self, decoder: decoder)
     var options: Options = []
 
     func decode(option: @autoclosure () -> Options, forKey key: CodingKeys) throws {
@@ -1370,3 +1380,37 @@ extension ApolloCodegenConfiguration.OutputOptions {
     }
   }
 }
+
+private struct AnyCodingKey: CodingKey {
+  var stringValue: String
+
+  init?(stringValue: String) {
+    self.stringValue = stringValue
+  }
+
+  var intValue: Int?
+
+  init?(intValue: Int) {
+    self.intValue = intValue
+    self.stringValue = "\(intValue)"
+  }
+}
+
+private func throwIfContainsUnexpectedKey<T, C: CodingKey & CaseIterable>(
+  container: KeyedDecodingContainer<C>,
+  type: T.Type,
+  decoder: Decoder
+) throws {
+  // Map all keys from the input object
+  let allKeys = Set(try decoder.container(keyedBy: AnyCodingKey.self).allKeys.map(\.stringValue))
+  // Map all valid keys from the given `CodingKey` enum
+  let validKeys = Set(C.allCases.map(\.stringValue))
+  guard allKeys.isSubset(of: validKeys) else {
+    let invalidKeys = allKeys.subtracting(validKeys).sorted()
+    throw DecodingError.typeMismatch(type, DecodingError.Context.init(
+      codingPath: container.codingPath,
+      debugDescription: "Unrecognized \(invalidKeys.count > 1 ? "keys" : "key") found: \(invalidKeys.joined(separator: ", "))",
+      underlyingError: nil
+    ))
+  }
+}
diff --git a/Tests/ApolloCodegenTests/ApolloCodegenConfigurationCodableTests.swift b/Tests/ApolloCodegenTests/ApolloCodegenConfigurationCodableTests.swift
index 6ebf0b7f0..733be12b3 100644
--- a/Tests/ApolloCodegenTests/ApolloCodegenConfigurationCodableTests.swift
+++ b/Tests/ApolloCodegenTests/ApolloCodegenConfigurationCodableTests.swift
@@ -923,4 +923,196 @@ class ApolloCodegenConfigurationCodableTests: XCTestCase {
       ))
     )
   }
+
+  func test__decodeApolloCodegenConfiguration__withInvalidFileOutput() throws {
+    // given
+    let subject = """
+    {
+      "schemaName": "MySchema",
+      "input": {
+        "operationSearchPaths": ["/search/path/**/*.graphql"],
+        "schemaSearchPaths": ["/path/to/schema.graphqls"]
+      },
+      "output": {
+        "testMocks": {
+          "none": {}
+        },
+        "schemaTypes": {
+          "path": "./MySchema",
+          "moduleType": {
+            "swiftPackageManager": {}
+          }
+        },
+        "operations": {
+          "inSchemaModule": {}
+        },
+        "options": {
+          "selectionSetInitializers" : {
+            "operations": true,
+            "namedFragments": true,
+            "localCacheMutations" : true
+          },
+          "queryStringLiteralFormat": "multiline",
+          "schemaDocumentation": "include",
+          "apqs": "disabled",
+          "warningsOnDeprecatedUsage": "include"
+        }
+      }
+    }
+    """.asData
+
+    func decodeConfiguration(subject: Data) throws -> ApolloCodegenConfiguration {
+      try JSONDecoder().decode(ApolloCodegenConfiguration.self, from: subject)
+    }
+    XCTAssertThrowsError(try decodeConfiguration(subject: subject)) { error in
+      guard case let DecodingError.typeMismatch(type, context) = error else { return fail("Incorrect error type") }
+      XCTAssertEqual("\(type)", String(describing: ApolloCodegenConfiguration.FileOutput.self))
+      XCTAssertEqual(context.debugDescription, "Unrecognized key found: options")
+    }
+  }
+
+  func test__decodeApolloCodegenConfiguration__withInvalidOptions() throws {
+    // given
+    let subject = """
+    {
+      "schemaName": "MySchema",
+      "input": {
+        "operationSearchPaths": ["/search/path/**/*.graphql"],
+        "schemaSearchPaths": ["/path/to/schema.graphqls"]
+      },
+      "output": {
+        "testMocks": {
+          "none": {}
+        },
+        "schemaTypes": {
+          "path": "./MySchema",
+          "moduleType": {
+            "swiftPackageManager": {}
+          }
+        },
+        "operations": {
+          "inSchemaModule": {}
+        }
+      },
+      "options": {
+        "secret_feature": "flappy_bird",
+        "selectionSetInitializers" : {
+          "operations": true,
+          "namedFragments": true,
+          "localCacheMutations" : true
+        },
+        "queryStringLiteralFormat": "multiline",
+        "schemaDocumentation": "include",
+        "apqs": "disabled",
+        "warningsOnDeprecatedUsage": "include"
+      }
+    }
+    """.asData
+
+    func decodeConfiguration(subject: Data) throws -> ApolloCodegenConfiguration {
+      try JSONDecoder().decode(ApolloCodegenConfiguration.self, from: subject)
+    }
+    XCTAssertThrowsError(try decodeConfiguration(subject: subject)) { error in
+      guard case let DecodingError.typeMismatch(type, context) = error else { return fail("Incorrect error type") }
+      XCTAssertEqual("\(type)", String(describing: ApolloCodegenConfiguration.OutputOptions.self))
+      XCTAssertEqual(context.debugDescription, "Unrecognized key found: secret_feature")
+    }
+  }
+
+  func test__decodeApolloCodegenConfiguration__withInvalidBaseConfiguration() throws {
+    // given
+    let subject = """
+    {
+      "contact_info": "42 Wallaby Way, Sydney",
+      "schemaName": "MySchema",
+      "input": {
+        "operationSearchPaths": ["/search/path/**/*.graphql"],
+        "schemaSearchPaths": ["/path/to/schema.graphqls"]
+      },
+      "output": {
+        "testMocks": {
+          "none": {}
+        },
+        "schemaTypes": {
+          "path": "./MySchema",
+          "moduleType": {
+            "swiftPackageManager": {}
+          }
+        },
+        "operations": {
+          "inSchemaModule": {}
+        }
+      },
+      "options": {
+        "selectionSetInitializers" : {
+          "operations": true,
+          "namedFragments": true,
+          "localCacheMutations" : true
+        },
+        "queryStringLiteralFormat": "multiline",
+        "schemaDocumentation": "include",
+        "apqs": "disabled",
+        "warningsOnDeprecatedUsage": "include"
+      }
+    }
+    """.asData
+
+    func decodeConfiguration(subject: Data) throws -> ApolloCodegenConfiguration {
+      try JSONDecoder().decode(ApolloCodegenConfiguration.self, from: subject)
+    }
+    XCTAssertThrowsError(try decodeConfiguration(subject: subject)) { error in
+      guard case let DecodingError.typeMismatch(type, context) = error else { return fail("Incorrect error type") }
+      XCTAssertEqual("\(type)", String(describing: ApolloCodegenConfiguration.self))
+      XCTAssertEqual(context.debugDescription, "Unrecognized key found: contact_info")
+    }
+  }
+
+  func test__decodeApolloCodegenConfiguration__withInvalidBaseConfiguration_multipleErrors() throws {
+    // given
+    let subject = """
+    {
+      "contact_info": "42 Wallaby Way, Sydney",
+      "motto": "Just keep swimming",
+      "schemaName": "MySchema",
+      "input": {
+        "operationSearchPaths": ["/search/path/**/*.graphql"],
+        "schemaSearchPaths": ["/path/to/schema.graphqls"]
+      },
+      "output": {
+        "testMocks": {
+          "none": {}
+        },
+        "schemaTypes": {
+          "path": "./MySchema",
+          "moduleType": {
+            "swiftPackageManager": {}
+          }
+        },
+        "operations": {
+          "inSchemaModule": {}
+        }
+      },
+      "options": {
+        "selectionSetInitializers" : {
+          "operations": true,
+          "namedFragments": true,
+          "localCacheMutations" : true
+        },
+        "queryStringLiteralFormat": "multiline",
+        "schemaDocumentation": "include",
+        "apqs": "disabled",
+        "warningsOnDeprecatedUsage": "include"
+      }
+    }
+    """.asData
+
+    func decodeConfiguration(subject: Data) throws -> ApolloCodegenConfiguration {
+      try JSONDecoder().decode(ApolloCodegenConfiguration.self, from: subject)
+    }
+    XCTAssertThrowsError(try decodeConfiguration(subject: subject)) { error in
+      guard case let DecodingError.typeMismatch(type, context) = error else { return fail("Incorrect error type") }
+      XCTAssertEqual("\(type)", String(describing: ApolloCodegenConfiguration.self))
+      XCTAssertEqual(context.debugDescription, "Unrecognized keys found: contact_info, motto")
+    }
+  }
 }