diff --git a/.travis.yml b/.travis.yml
index 928b418..fd4905e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -11,6 +11,7 @@ php:
   - 5.6
   - 7.0
   - 7.1
+  - 7.2
   - hhvm
 
 env:
diff --git a/src/PromiseCore.php b/src/PromiseCore.php
index dbc89f6..4e6f571 100644
--- a/src/PromiseCore.php
+++ b/src/PromiseCore.php
@@ -76,8 +76,8 @@ public function __construct(
         $handle,
         ResponseBuilder $responseBuilder
     ) {
-        assert('is_resource($handle)');
-        assert('get_resource_type($handle) === "curl"');
+        assert(is_resource($handle));
+        assert(get_resource_type($handle) === "curl");
 
         $this->request = $request;
         $this->handle = $handle;