diff --git a/psalm.xml.dist b/psalm.xml.dist
index 1fdcb9cb4d3..5ca67684de5 100644
--- a/psalm.xml.dist
+++ b/psalm.xml.dist
@@ -86,6 +86,7 @@
         <PossiblyUnusedMethod>
             <errorLevel type="suppress">
                 <directory name="tests" />
+                <directory name="src/Psalm/PluginApi" />
                 <file name="src/Psalm/Plugin.php" />
                 <referencedMethod name="Psalm\Codebase::getParentInterfaces" />
                 <referencedMethod name="Psalm\Codebase::getMethodParams" />
diff --git a/src/Psalm/Config.php b/src/Psalm/Config.php
index 493f5218d21..e3d7753d389 100644
--- a/src/Psalm/Config.php
+++ b/src/Psalm/Config.php
@@ -750,8 +750,6 @@ public function initializePlugins(ProjectChecker $project_checker)
             }
         }
 
-        $codebase = $project_checker->codebase;
-
         foreach ($this->filetype_scanner_paths as $extension => $path) {
             $fq_class_name = $this->getPluginClassForPath($project_checker, $path, 'Psalm\\Scanner\\FileScanner');
 
@@ -771,33 +769,12 @@ public function initializePlugins(ProjectChecker $project_checker)
         }
 
         foreach ($this->plugin_paths as $path) {
-            $fq_class_name = $this->getPluginClassForPath($project_checker, $path, 'Psalm\\Plugin');
-
-            /** @psalm-suppress UnresolvableInclude */
-            require_once($path);
-
-            if ($codebase->methods->methodExists($fq_class_name . '::afterMethodCallCheck')) {
-                $this->after_method_checks[$fq_class_name] = $fq_class_name;
-            }
-
-            if ($codebase->methods->methodExists($fq_class_name . '::afterFunctionCallCheck')) {
-                $this->after_function_checks[$fq_class_name] = $fq_class_name;
-            }
-
-            if ($codebase->methods->methodExists($fq_class_name . '::afterExpressionCheck')) {
-                $this->after_expression_checks[$fq_class_name] = $fq_class_name;
-            }
-
-            if ($codebase->methods->methodExists($fq_class_name . '::afterStatementCheck')) {
-                $this->after_statement_checks[$fq_class_name] = $fq_class_name;
-            }
-
-            if ($codebase->methods->methodExists($fq_class_name . '::afterClassLikeExistsCheck')) {
-                $this->after_classlike_exists_checks[$fq_class_name] = $fq_class_name;
-            }
-
-            if ($codebase->methods->methodExists($fq_class_name . '::afterVisitClassLike')) {
-                $this->after_visit_classlikes[$fq_class_name] = $fq_class_name;
+            try {
+                $plugin_object = new LegacyPlugin($path, $this, $project_checker);
+                $plugin_object($facade);
+            } catch (\Throwable $e) {
+                // todo: ???
+                throw $e;
             }
         }
     }
diff --git a/src/Psalm/LegacyPlugin.php b/src/Psalm/LegacyPlugin.php
new file mode 100644
index 00000000000..4ef0e5e82e1
--- /dev/null
+++ b/src/Psalm/LegacyPlugin.php
@@ -0,0 +1,99 @@
+<?php
+namespace Psalm;
+
+use Psalm\Checker\ClassLikeChecker;
+use Psalm\Checker\ProjectChecker;
+use Psalm\Scanner\FileScanner;
+
+class LegacyPlugin
+{
+    /** @var string */
+    private $path;
+
+    /** @var ProjectChecker */
+    private $project_checker;
+
+    /** @var Config */
+    private $config;
+
+    public function __construct(string $path, Config $config, ProjectChecker $project_checker)
+    {
+        $this->path = $path;
+        $this->config = $config;
+        $this->project_checker = $project_checker;
+    }
+
+    public function __invoke(PluginApi\RegistrationInterface $api): void
+    {
+        $codebase = $this->project_checker->codebase;
+        $fq_class_name = $this->getPluginClassForPath($this->path, Plugin::class);
+
+        /** @psalm-suppress UnresolvableInclude */
+        require_once($this->path);
+
+        if ($codebase->methods->methodExists($fq_class_name . '::afterMethodCallCheck')) {
+            $this->config->after_method_checks[$fq_class_name] = $fq_class_name;
+        }
+
+        if ($codebase->methods->methodExists($fq_class_name . '::afterFunctionCallCheck')) {
+            $this->config->after_function_checks[$fq_class_name] = $fq_class_name;
+        }
+
+        if ($codebase->methods->methodExists($fq_class_name . '::afterExpressionCheck')) {
+            $this->config->after_expression_checks[$fq_class_name] = $fq_class_name;
+        }
+
+        if ($codebase->methods->methodExists($fq_class_name . '::afterStatementCheck')) {
+            $this->config->after_statement_checks[$fq_class_name] = $fq_class_name;
+        }
+
+        if ($codebase->methods->methodExists($fq_class_name . '::afterClassLikeExistsCheck')) {
+            $this->config->after_classlike_exists_checks[$fq_class_name] = $fq_class_name;
+        }
+
+        if ($codebase->methods->methodExists($fq_class_name . '::afterVisitClassLike')) {
+            $this->config->after_visit_classlikes[$fq_class_name] = $fq_class_name;
+        }
+    }
+
+    /**
+     * @param  string $path
+     * @param  string $must_extend
+     *
+     * @return string
+     */
+    private function getPluginClassForPath(string $path, string $must_extend)
+    {
+        $codebase = $this->project_checker->codebase;
+
+        $file_storage = $codebase->createFileStorageForPath($path);
+        $file_to_scan = new FileScanner($path, $this->config->shortenFileName($path), true);
+        $file_to_scan->scan(
+            $codebase,
+            $file_storage
+        );
+
+        $declared_classes = ClassLikeChecker::getClassesForFile($this->project_checker, $path);
+
+        if (count($declared_classes) !== 1) {
+            throw new \InvalidArgumentException(
+                'Plugins must have exactly one class in the file - ' . $path . ' has ' .
+                    count($declared_classes)
+            );
+        }
+
+        $fq_class_name = reset($declared_classes);
+
+        if (!$codebase->classExtends(
+            $fq_class_name,
+            $must_extend
+        )
+        ) {
+            throw new \InvalidArgumentException(
+                'This plugin must extend ' . $must_extend . ' - ' . $path . ' does not'
+            );
+        }
+
+        return $fq_class_name;
+    }
+}
diff --git a/src/Psalm/PluginApi/RegistrationInterface.php b/src/Psalm/PluginApi/RegistrationInterface.php
new file mode 100644
index 00000000000..0592e0d4e99
--- /dev/null
+++ b/src/Psalm/PluginApi/RegistrationInterface.php
@@ -0,0 +1,7 @@
+<?php
+namespace Psalm\PluginApi;
+
+interface RegistrationInterface
+{
+    public function addStubFile(string $file_name): void;
+}
diff --git a/src/Psalm/PluginFacade.php b/src/Psalm/PluginFacade.php
index 354cab99ba3..5e9d2598898 100644
--- a/src/Psalm/PluginFacade.php
+++ b/src/Psalm/PluginFacade.php
@@ -1,10 +1,8 @@
 <?php
 namespace Psalm;
+use Psalm\PluginApi\RegistrationInterface;
 
-/**
- * Represents the API available to plugins
- */
-class PluginFacade
+class PluginFacade implements RegistrationInterface
 {
     /**
      * @var Config