diff --git a/config.xsd b/config.xsd
index 2f3c6f059..373bb2094 100644
--- a/config.xsd
+++ b/config.xsd
@@ -144,6 +144,7 @@
             <xs:element name="DuplicateArrayKey" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="DuplicateParam" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="DuplicateClass" type="IssueHandlerType" minOccurs="0" />
+            <xs:element name="DuplicateMethod" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="EmptyArrayAccess" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="FalseOperand" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="FalsableReturnStatement" type="IssueHandlerType" minOccurs="0" />
diff --git a/docs/issues.md b/docs/issues.md
index 1f85d1807..e36a4f2a9 100644
--- a/docs/issues.md
+++ b/docs/issues.md
@@ -180,6 +180,17 @@ class A {}
 class A {}
 ```
 
+### DuplicateMethod
+
+Emitted when a method is defined twice
+
+```php
+class A {
+    public function foo() {}
+    public function foo() {}
+}
+```
+
 ### DuplicateParam
 
 Emitted when a function has a param defined twice
diff --git a/src/Psalm/Config.php b/src/Psalm/Config.php
index f5ff851cf..5c7c37503 100644
--- a/src/Psalm/Config.php
+++ b/src/Psalm/Config.php
@@ -497,7 +497,13 @@ class Config
         }
 
         if (isset($config_xml['autoloader'])) {
-            $config->autoloader = (string) $config_xml['autoloader'];
+            $autoloader_path = $config->base_dir . DIRECTORY_SEPARATOR . $config_xml['autoloader'];
+
+            if (!file_exists($autoloader_path)) {
+                throw new ConfigException('Cannot locate config schema');
+            }
+
+            $config->autoloader = realpath($autoloader_path);
         }
 
         if (isset($config_xml['cacheDirectory'])) {
@@ -1331,7 +1337,7 @@ class Config
 
         if ($this->autoloader) {
             // do this in a separate method so scope does not leak
-            $this->requireAutoloader($this->base_dir . DIRECTORY_SEPARATOR . $this->autoloader);
+            $this->requireAutoloader($this->autoloader);
 
             $this->collectPredefinedConstants();
             $this->collectPredefinedFunctions();
diff --git a/src/Psalm/Internal/Visitor/ReflectorVisitor.php b/src/Psalm/Internal/Visitor/ReflectorVisitor.php
index 754d99a63..68b0df840 100644
--- a/src/Psalm/Internal/Visitor/ReflectorVisitor.php
+++ b/src/Psalm/Internal/Visitor/ReflectorVisitor.php
@@ -21,6 +21,7 @@ use Psalm\Exception\IncorrectDocblockException;
 use Psalm\Exception\TypeParseTreeException;
 use Psalm\FileSource;
 use Psalm\Issue\DuplicateClass;
+use Psalm\Issue\DuplicateMethod;
 use Psalm\Issue\DuplicateParam;
 use Psalm\Issue\InvalidDocblock;
 use Psalm\Issue\MisplacedRequiredParam;
@@ -835,7 +836,7 @@ class ReflectorVisitor extends PhpParser\NodeVisitorAbstract implements PhpParse
      * @param  PhpParser\Node\FunctionLike $stmt
      * @param  bool $fake_method in the case of @method annotations we do something a little strange
      *
-     * @return FunctionLikeStorage
+     * @return FunctionLikeStorage|false
      */
     private function registerFunctionLike(PhpParser\Node\FunctionLike $stmt, $fake_method = false)
     {
@@ -889,7 +890,25 @@ class ReflectorVisitor extends PhpParser\NodeVisitorAbstract implements PhpParse
 
             if (isset($class_storage->methods[strtolower($stmt->name->name)])) {
                 if (!$this->codebase->register_stub_files) {
-                    throw new \InvalidArgumentException('Cannot re-register ' . $function_id);
+                    $duplicate_method_storage = $class_storage->methods[strtolower($stmt->name->name)];
+
+                    if (IssueBuffer::accepts(
+                        new DuplicateMethod(
+                            'Method ' . $function_id . ' has already been defined'
+                                . ($duplicate_method_storage->location
+                                    ? ' in ' . $duplicate_method_storage->location->file_path
+                                    : ''),
+                            new CodeLocation($this->file_scanner, $stmt, null, true)
+                        )
+                    )) {
+                        // fall through
+                    }
+
+                    $this->file_storage->has_visitor_issues = true;
+
+                    $duplicate_method_storage->has_visitor_issues = true;
+
+                    return false;
                 }
 
                 $storage = $class_storage->methods[strtolower($stmt->name->name)];
diff --git a/src/Psalm/Issue/DuplicateMethod.php b/src/Psalm/Issue/DuplicateMethod.php
new file mode 100644
index 000000000..8ce64ef50
--- /dev/null
+++ b/src/Psalm/Issue/DuplicateMethod.php
@@ -0,0 +1,6 @@
+<?php
+namespace Psalm\Issue;
+
+class DuplicateMethod extends CodeIssue
+{
+}
diff --git a/src/Psalm/IssueBuffer.php b/src/Psalm/IssueBuffer.php
index e22cfc656..fe7a8c386 100644
--- a/src/Psalm/IssueBuffer.php
+++ b/src/Psalm/IssueBuffer.php
@@ -4,6 +4,8 @@ namespace Psalm;
 use Psalm\Internal\Analyzer\ProjectAnalyzer;
 use Psalm\Issue\ClassIssue;
 use Psalm\Issue\CodeIssue;
+use Psalm\Issue\DuplicateClass;
+use Psalm\Issue\DuplicateMethod;
 use Psalm\Issue\MethodIssue;
 use Psalm\Issue\PropertyIssue;
 use Psalm\Output\Compact;
@@ -61,7 +63,10 @@ class IssueBuffer
             return false;
         }
 
-        if (!$config->reportIssueInFile($issue_type, $e->getFilePath())) {
+        if (!$e instanceof DuplicateClass
+            && !$e instanceof DuplicateMethod
+            && !$config->reportIssueInFile($issue_type, $e->getFilePath())
+        ) {
             return false;
         }
 
diff --git a/tests/ClassStringTest.php b/tests/ClassStringTest.php
index 805ff3bd1..9b781cb14 100644
--- a/tests/ClassStringTest.php
+++ b/tests/ClassStringTest.php
@@ -288,6 +288,17 @@ class ClassStringTest extends TestCase
                         use T;
                     }'
             ],
+            'refineStringToClassString' => [
+                '<?php
+                    class A {}
+
+                    function foo(string $s) : void {
+                        if ($s !== A::class) {
+                            return;
+                        }
+                        new $s();
+                    }',
+            ],
         ];
     }
 
diff --git a/tests/FileUpdates/ErrorAfterUpdateTest.php b/tests/FileUpdates/ErrorAfterUpdateTest.php
index 6a64c77b2..ebd616878 100644
--- a/tests/FileUpdates/ErrorAfterUpdateTest.php
+++ b/tests/FileUpdates/ErrorAfterUpdateTest.php
@@ -93,17 +93,15 @@ class ErrorAfterUpdateTest extends \Psalm\Tests\TestCase
             $this->file_provider->registerFile($file_path, $contents);
         }
 
+        $this->expectException('\Psalm\Exception\CodeException');
+        $this->expectExceptionMessageRegexp('/\b' . preg_quote($error_message, '/') . '\b/');
+
         $codebase->reloadFiles($this->project_analyzer, array_keys($end_files));
 
         foreach ($end_files as $file_path => $_) {
             $codebase->addFilesToAnalyze([$file_path => $file_path]);
         }
 
-        $codebase->scanFiles();
-
-        $this->expectException('\Psalm\Exception\CodeException');
-        $this->expectExceptionMessageRegexp('/\b' . preg_quote($error_message, '/') . '\b/');
-
         $codebase->analyzer->analyzeFiles($this->project_analyzer, 1, false);
     }
 
@@ -556,6 +554,46 @@ class ErrorAfterUpdateTest extends \Psalm\Tests\TestCase
                 ],
                 'error_message' => 'PropertyNotSetInConstructor'
             ],
+            'duplicateClass' => [
+                'file_stages' => [
+                    [
+                        getcwd() . DIRECTORY_SEPARATOR . 'A.php' => '<?php
+                            namespace Foo;
+
+                            class A {}',
+                    ],
+                    [
+                        getcwd() . DIRECTORY_SEPARATOR . 'A.php' => '<?php
+                            namespace Foo;
+
+                            class A {}
+                            class A {}',
+                    ],
+                ],
+                'error_message' => 'DuplicateClass'
+            ],
+            'duplicateMethod' => [
+                'file_stages' => [
+                    [
+                        getcwd() . DIRECTORY_SEPARATOR . 'A.php' => '<?php
+                            namespace Foo;
+
+                            class A {
+                                public function foo() : void {}
+                            }',
+                    ],
+                    [
+                        getcwd() . DIRECTORY_SEPARATOR . 'A.php' => '<?php
+                            namespace Foo;
+
+                            class A {
+                                public function foo() : void {}
+                                public function foo() : void {}
+                            }',
+                    ],
+                ],
+                'error_message' => 'DuplicateMethod'
+            ],
         ];
     }
 }
diff --git a/tests/performance/diff_parse_large_file.php b/tests/performance/diff_parse_large_file.php
index 83ee6d6fc..5539670fa 100644
--- a/tests/performance/diff_parse_large_file.php
+++ b/tests/performance/diff_parse_large_file.php
@@ -2,7 +2,7 @@
 
 ini_set('display_startup_errors', '1');
 ini_set('html_errors', '1');
-ini_set('memory_limit', '-1');
+ini_set('memory_limit', '4G');
 error_reporting(E_ALL);
 
 gc_disable();
@@ -44,3 +44,7 @@ Psalm\Internal\Provider\StatementsProvider::parseStatements($b);
 $diff_2 = microtime(true) - $time;
 
 echo 'Full parsing: ' . number_format($diff_2, 4) . "\n";
+
+echo strlen($a);
+
+Psalm\Internal\Diff\FileDiffer::getDiff($a, '');