diff --git a/src/lint/linter/ArcanistXHPASTLinter.php b/src/lint/linter/ArcanistXHPASTLinter.php
--- a/src/lint/linter/ArcanistXHPASTLinter.php
+++ b/src/lint/linter/ArcanistXHPASTLinter.php
@@ -4133,7 +4133,7 @@
         $function_name,
         self::LINT_ALIAS_FUNCTION,
         pht('Alias functions should be avoided.'),
-        $aliases[$function_name->getConcreteString()]);
+        $aliases[phutil_utf8_strtolower($function_name->getConcreteString())]);
     }
   }
 
diff --git a/src/lint/linter/__tests__/xhpast/alias-functions.lint-test b/src/lint/linter/__tests__/xhpast/alias-functions.lint-test
--- a/src/lint/linter/__tests__/xhpast/alias-functions.lint-test
+++ b/src/lint/linter/__tests__/xhpast/alias-functions.lint-test
@@ -3,12 +3,15 @@
 $x = array();
 sizeof($x);
 die();
+sizeOf($x);
 ~~~~~~~~~~
 advice:4:1
 advice:5:1
+advice:6:1
 ~~~~~~~~~~
 <?php
 
 $x = array();
 count($x);
 exit();
+count($x);