diff --git a/config.xsd b/config.xsd
index a2412ca10..012ce9873 100644
--- a/config.xsd
+++ b/config.xsd
@@ -10,6 +10,7 @@
     <xs:complexType name="PsalmType">
         <xs:choice maxOccurs="unbounded">
             <xs:element name="projectFiles" type="ProjectFilesType" minOccurs="1" maxOccurs="1" />
+            <xs:element name="extraFiles" type="ProjectFilesType" minOccurs="0" maxOccurs="1" />
             <xs:element name="taintAnalysis" type="TaintAnalysisType" minOccurs="0" maxOccurs="1" />
             <xs:element name="fileExtensions" type="FileExtensionsType" minOccurs="0" maxOccurs="1" />
             <xs:element name="mockClasses" type="MockClassesType" minOccurs="0" maxOccurs="1" />
diff --git a/src/Psalm/Config.php b/src/Psalm/Config.php
index 8b9f7015a..33f11a8a5 100644
--- a/src/Psalm/Config.php
+++ b/src/Psalm/Config.php
@@ -183,6 +183,11 @@ class Config
      */
     protected $project_files;
 
+    /**
+     * @var ProjectFileFilter|null
+     */
+    protected $extra_files;
+
     /**
      * The base directory of this config file
      *
@@ -908,6 +913,10 @@ class Config
             $config->project_files = ProjectFileFilter::loadFromXMLElement($config_xml->projectFiles, $base_dir, true);
         }
 
+        if (isset($config_xml->extraFiles)) {
+            $config->extra_files = ProjectFileFilter::loadFromXMLElement($config_xml->extraFiles, $base_dir, true);
+        }
+
         if (isset($config_xml->taintAnalysis->ignoreFiles)) {
             $config->taint_analysis_ignored_files = TaintAnalysisFileFilter::loadFromXMLElement(
                 $config_xml->taintAnalysis->ignoreFiles,
@@ -1361,6 +1370,16 @@ class Config
         return $this->project_files && $this->project_files->allows($file_path);
     }
 
+    /**
+     * @param   string $file_path
+     *
+     * @return  bool
+     */
+    public function isInExtraDirs($file_path)
+    {
+        return $this->extra_files && $this->extra_files->allows($file_path);
+    }
+
     /**
      * @param   string $file_path
      *
@@ -1630,6 +1649,18 @@ class Config
         return $this->project_files->getFiles();
     }
 
+    /**
+     * @return array<string>
+     */
+    public function getExtraDirectories()
+    {
+        if (!$this->extra_files) {
+            return [];
+        }
+
+        return $this->extra_files->getDirectories();
+    }
+
     /**
      * @param   string $file_path
      *
diff --git a/src/Psalm/Internal/Analyzer/ProjectAnalyzer.php b/src/Psalm/Internal/Analyzer/ProjectAnalyzer.php
index 4c1c310cf..5365ba5bc 100644
--- a/src/Psalm/Internal/Analyzer/ProjectAnalyzer.php
+++ b/src/Psalm/Internal/Analyzer/ProjectAnalyzer.php
@@ -177,6 +177,11 @@ class ProjectAnalyzer
      */
     private $project_files = [];
 
+    /**
+     * @var array<string,string>
+     */
+    private $extra_files = [];
+
     /**
      * @var array<string, string>
      */
@@ -267,9 +272,9 @@ class ProjectAnalyzer
         $this->stdout_report_options = $stdout_report_options;
         $this->generated_report_options = $generated_report_options;
 
-        foreach ($this->config->getProjectDirectories() as $dir_name) {
-            $file_extensions = $this->config->getFileExtensions();
+        $file_extensions = $this->config->getFileExtensions();
 
+        foreach ($this->config->getProjectDirectories() as $dir_name) {
             $file_paths = $this->file_provider->getFilesInDir($dir_name, $file_extensions);
 
             foreach ($file_paths as $file_path) {
@@ -279,6 +284,16 @@ class ProjectAnalyzer
             }
         }
 
+        foreach ($this->config->getExtraDirectories() as $dir_name) {
+            $file_paths = $this->file_provider->getFilesInDir($dir_name, $file_extensions);
+
+            foreach ($file_paths as $file_path) {
+                if ($this->config->isInExtraDirs($file_path)) {
+                    $this->addExtraFile($file_path);
+                }
+            }
+        }
+
         foreach ($this->config->getProjectFiles() as $file_path) {
             $this->addProjectFile($file_path);
         }
@@ -548,6 +563,7 @@ class ProjectAnalyzer
         ) {
             $this->visitAutoloadFiles();
 
+            $this->codebase->scanner->addFilesToShallowScan($this->extra_files);
             $this->codebase->scanner->addFilesToDeepScan($this->project_files);
             $this->codebase->analyzer->addFilesToAnalyze($this->project_files);
 
@@ -1050,6 +1066,10 @@ class ProjectAnalyzer
         $this->project_files[$file_path] = $file_path;
     }
 
+    public function addExtraFile(string $file_path) : void
+    {
+        $this->extra_files[$file_path] = $file_path;
+    }
 
     /**
      * @param  string $dir_name