diff --git a/lib/helpers.dart b/lib/helpers.dart
index a6cae357..770e37c3 100644
--- a/lib/helpers.dart
+++ b/lib/helpers.dart
@@ -271,9 +271,6 @@ GraphQLSchema schemaFromJsonString(String jsonS) =>
 
 Future<String> generate(
     GraphQLSchema schema, String path, GeneratorOptions options) async {
-  assert(schema != null, 'Schema can\'t be null.');
-  assert(path != null, 'Input file can\'t be null.');
-
   final basename = p.basenameWithoutExtension(path);
   final customParserImport = options.customParserImport != null
       ? '  import \'${options.customParserImport}\';'
diff --git a/lib/schema/graphql.dart b/lib/schema/graphql.dart
index fb3600f8..529a5d29 100644
--- a/lib/schema/graphql.dart
+++ b/lib/schema/graphql.dart
@@ -30,7 +30,7 @@ class GraphQLSchema {
         json != null &&
             json['data'] != null &&
             json['data']['__schema'] != null,
-        'JSON schema file must be the output of a Introspection Query.');
+        'JSON schema file must be the output of an Introspection Query.');
     return _$GraphQLSchemaFromJson(json['data']['__schema']);
   }
 
diff --git a/test/builder_test.dart b/test/builder_test.dart
index 186fab6f..3af5974c 100644
--- a/test/builder_test.dart
+++ b/test/builder_test.dart
@@ -49,5 +49,20 @@ void main() {
         'a|lib/schemas/project5.api.dart': emptyGeneratorResponse('project5'),
       });
     });
+
+    test(
+        'A .schema.json file must be an Introspection Query response, or generator will throw',
+        () async {
+      expect(testBuilder(builder, {'a|lib/api.schema.json': '{}'}),
+          throwsA(TypeMatcher<AssertionError>()));
+
+      expect(testBuilder(builder, {'a|lib/api.schema.json': '{"data": {}}'}),
+          throwsA(TypeMatcher<AssertionError>()));
+
+      expect(
+          testBuilder(
+              builder, {'a|lib/api.schema.json': 'not even a json file'}),
+          throwsA(TypeMatcher<FormatException>()));
+    });
   });
 }