diff --git a/lib/linguist/heuristics.rb b/lib/linguist/heuristics.rb
index 4c1bf295..e1b520b4 100644
--- a/lib/linguist/heuristics.rb
+++ b/lib/linguist/heuristics.rb
@@ -25,6 +25,9 @@ module Linguist
         if languages.all? { |l| ["Common Lisp", "OpenCL"].include?(l) }
           result = disambiguate_cl(data, languages)
         end
+        if languages.all? { |l| ["Hack", "PHP"].include?(l) }
+          result = disambiguate_hack(data, languages)
+        end
         return result
       end
     end
@@ -88,6 +91,13 @@ module Linguist
       matches
     end
 
+    def self.disambiguate_hack(data, languages)
+      matches = []
+      matches << Language["Hack"] if data.include?("<?hh")
+      matches << Language["PHP"] if /<?[^h]/.match(data)
+      matches
+    end
+
     def self.active?
       !!ACTIVE
     end
diff --git a/lib/linguist/languages.yml b/lib/linguist/languages.yml
index 11f372c4..1b22c713 100644
--- a/lib/linguist/languages.yml
+++ b/lib/linguist/languages.yml
@@ -986,6 +986,7 @@ Hack:
   ace_mode: php
   extensions:
   - .hh
+  - .php
 
 Haml:
   group: HTML
diff --git a/samples/Hack/funs.php b/samples/Hack/funs.php
new file mode 100644
index 00000000..a374d367
--- /dev/null
+++ b/samples/Hack/funs.php
@@ -0,0 +1,32 @@
+<?hh
+/**
+ * Copyright (c) 2014, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ */
+
+/**
+ * This file contains a bunch of php stubs for functions that have been added
+ * to hhvm (though aren't in a release yet). These are important because the
+ * Hack typechecker can understand them
+ */
+
+class InvariantViolationException extends Exception {}
+
+function invariant(mixed $test, string $message): void {
+  if (!$test) {
+    invariant_violation($message);
+  }
+}
+
+function invariant_violation(string $message): void {
+  throw new InvariantViolationException($message);
+}
+
+function class_meth(string $class, string $method) {
+  return array($class, $method);
+}
\ No newline at end of file