diff --git a/src/lint/linter/ArcanistCSSLintLinter.php b/src/lint/linter/ArcanistCSSLintLinter.php
--- a/src/lint/linter/ArcanistCSSLintLinter.php
+++ b/src/lint/linter/ArcanistCSSLintLinter.php
@@ -24,7 +24,7 @@
   }
 
   public function getMandatoryFlags() {
-    return '--format=lint-xml';
+    return array('--format=lint-xml');
   }
 
   public function getDefaultFlags() {
diff --git a/src/lint/linter/ArcanistExternalLinter.php b/src/lint/linter/ArcanistExternalLinter.php
--- a/src/lint/linter/ArcanistExternalLinter.php
+++ b/src/lint/linter/ArcanistExternalLinter.php
@@ -15,7 +15,7 @@
   private $flags;
 
 
-/* -(  Interpreters, Binaries and Flags  )----------------------------------- */
+/* -(  Interpreters, Binaries and ar  )----------------------------------- */
 
 
   /**
@@ -117,11 +117,11 @@
    * Flags which are not mandatory should be provided in
    * @{method:getDefaultFlags} instead.
    *
-   * @return string|null  Mandatory flags, like `"--format=xml"`.
+   * @return list<string>  Mandatory flags, like `"--format=xml"`.
    * @task bin
    */
   protected function getMandatoryFlags() {
-    return null;
+    return array();
   }
 
 
@@ -133,11 +133,11 @@
    *
    * Default flags can be overridden with @{method:setFlags}.
    *
-   * @return string|null  Overridable default flags.
+   * @return list<string>  Overridable default flags.
    * @task bin
    */
   protected function getDefaultFlags() {
-    return null;
+    return array();
   }
 
 
@@ -145,7 +145,7 @@
    * Override default flags with custom flags. If not overridden, flags provided
    * by @{method:getDefaultFlags} are used.
    *
-   * @param string New flags.
+   * @param list<string>|string New flags.
    * @return this
    * @task bin
    */
@@ -352,10 +352,9 @@
    * @task exec
    */
   protected function getCommandFlags() {
-    return csprintf(
-      '%C %C',
-      $this->getMandatoryFlags(),
-      coalesce($this->flags, $this->getDefaultFlags()));
+    return implode(' ', array_merge(
+      (array) $this->getMandatoryFlags(),
+      (array) coalesce($this->flags, $this->getDefaultFlags())));
   }
 
 
@@ -410,7 +409,7 @@
   public function getLinterConfigurationOptions() {
     $options = array(
       'bin' => 'optional string | list<string>',
-      'flags' => 'optional string',
+      'flags' => 'optional string | list<string>',
     );
 
     if ($this->shouldUseInterpreter()) {
diff --git a/src/lint/linter/ArcanistFlake8Linter.php b/src/lint/linter/ArcanistFlake8Linter.php
--- a/src/lint/linter/ArcanistFlake8Linter.php
+++ b/src/lint/linter/ArcanistFlake8Linter.php
@@ -21,7 +21,7 @@
 
     $config = $this->getEngine()->getConfigurationManager();
 
-    $options = $config->getConfigFromAnySource('lint.flake8.options', '');
+    $options = $config->getConfigFromAnySource('lint.flake8.options', array());
 
     return $options;
   }
diff --git a/src/lint/linter/ArcanistPhpcsLinter.php b/src/lint/linter/ArcanistPhpcsLinter.php
--- a/src/lint/linter/ArcanistPhpcsLinter.php
+++ b/src/lint/linter/ArcanistPhpcsLinter.php
@@ -26,7 +26,7 @@
   }
 
   public function getMandatoryFlags() {
-    return '--report=xml';
+    return array('--report=xml');
   }
 
   public function getInstallInstructions() {
@@ -41,7 +41,13 @@
     $options = $config->getConfigFromAnySource('lint.phpcs.options');
 
     $standard = $config->getConfigFromAnySource('lint.phpcs.standard');
-    $options .= !empty($standard) ? ' --standard=' . $standard : '';
+    if (!empty($standard)) {
+      if (is_array($options)) {
+        $options[] = '--standard=' . $standard;
+      } else {
+        $options .= ' --standard=' . $standard;
+      }
+    }
 
     return $options;
   }
diff --git a/src/lint/linter/ArcanistRubyLinter.php b/src/lint/linter/ArcanistRubyLinter.php
--- a/src/lint/linter/ArcanistRubyLinter.php
+++ b/src/lint/linter/ArcanistRubyLinter.php
@@ -41,7 +41,7 @@
   protected function getMandatoryFlags() {
     // -w: turn on warnings
     // -c: check syntax
-    return '-w -c';
+    return array('-w', '-c');
   }
 
   protected function getDefaultMessageSeverity($code) {