diff --git a/potx.inc b/potx.inc
index 94af04a..5d98b11 100644
--- a/potx.inc
+++ b/potx.inc
@@ -212,9 +212,9 @@ function _potx_process_file($file_path, $strip_prefix = 0, $save_callback = '_po
     _potx_parse_twig_file($code, $file_name, $save_callback);
   }
 
-  $constraint_extract = false;
+  $constraint_extract = FALSE;
   if (substr($name_parts['filename'], -10) == 'Constraint' && $api_version > POTX_API_7) {
-    $constraint_extract = true;
+    $constraint_extract = TRUE;
   }
 
   // Extract raw PHP language tokens.
@@ -238,7 +238,7 @@ function _potx_process_file($file_path, $strip_prefix = 0, $save_callback = '_po
          if (in_array($token[0], array(T_STRING, T_DOC_COMMENT)) || ($token[0] == T_VARIABLE && $token[1] == '$t') || $constraint_match) {
 
            // Give doc comments a specific key because their content varies.
-           $key = ($token[0] == T_DOC_COMMENT) ? 'T_DOC_COMMENT' : ($constraint_match ? 'T_CONSTRAINT' : $token[1]);
+           $key = ($token[0] == T_DOC_COMMENT) ? 'T_DOC_COMMENT' : ($constraint_match ? 'T_POTX_CONSTRAINT' : $token[1]);
            if (!isset($_potx_lookup[$key])) {
              $_potx_lookup[$key] = array();
            }
@@ -1764,10 +1764,26 @@ function _potx_find_routing_yml_file_strings($code, $file_name, $save_callback,
   }
 }
 
+
+/**
+ * Detect validation constraint messages. Drupal 8+
+ *
+ * This sequences is searched for:
+ *   T_POTX_CONSTRAINT = T_CONSTANT_ENCAPSED_STRING
+ *
+ * note: T_POTX_CONSTRAINT is marked for T_VARIABLE tokens inside .php files
+ *   with the "Constraint" suffix, where the token is "$message", or ends
+ *   with "Message"
+ *
+ * @param $file_name
+ *   Name of file parsed.
+ * @param $save_callback
+ *   Callback function used to save strings.
+ */
 function _potx_find_constraint_messages($file_name, $save_callback) {
   global $_potx_tokens, $_potx_lookup;
 
-  foreach ($_potx_lookup['T_CONSTRAINT'] as $key => $ti) {
+  foreach ($_potx_lookup['T_POTX_CONSTRAINT'] as $key => $ti) {
 
     if ($_potx_tokens[$ti + 1] == '=' && $_potx_tokens[$ti + 2][0] == T_CONSTANT_ENCAPSED_STRING) {
       $str = $_potx_tokens[$ti + 2][1];
diff --git a/tests/TestConstraint.php b/tests/TestConstraint.php
new file mode 100644
index 0000000..8b93b74
--- /dev/null
+++ b/tests/TestConstraint.php
@@ -0,0 +1,8 @@
+<?php
+class TestConstraint {
+
+  public $message = 'Test message';extends Range
+  public $testMessage = 'Test message 2';
+  public $testPluralMessage = '1 test message|@count test message';
+  public $normalVar = 'Not a message for translation';
+}
diff --git a/tests/potx.test b/tests/potx.test
index 9e301a7..19315f9 100644
--- a/tests/potx.test
+++ b/tests/potx.test
@@ -281,6 +281,19 @@ class PotxTestCase extends DrupalWebTestCase {
     $this->assertNoMsgID('mapping');
     $this->assertNoMsgID('sequence');
   }
+  
+  /**
+   * Test parsing Drupal 8 validation constraint messages.
+   */
+  public function testDrupal8ConstraintMessages() {
+    $filename = drupal_get_path('module', 'potx') .'/tests/TestConstraint.php';
+    $this->parseFile($filename, POTX_API_8);
+    
+    $this->assertMsgID('Test message');
+    $this->assertMsgID('Test message 2');
+    $this->assertPluralID('1 test message', '@count test message');
+    $this->assertNoMsgID('Not a message for translation');
+  }
 
   /**
    * Test parsing of Drupal 6 info file. Drupal 5 and 7 have no other rules.