diff --git a/src/base.cc b/src/base.cc
index 2c7fcb5..9d3df0a 100644
--- a/src/base.cc
+++ b/src/base.cc
@@ -160,7 +160,11 @@ namespace php_arma
 
     void base_init()
     {
-        base_ce = interface_register<base_php_name>(zend_ce_countable);
+        base_ce = interface_register<base_php_name>(
+#if PHP_VERSION_ID >= 70200
+            zend_ce_countable
+#endif
+        );
     }
 
     PHP_ARMA_INSTANTIATE(base, mat);
diff --git a/src/constants.cc b/src/constants.cc
index cd7c790..fdf74a8 100644
--- a/src/constants.cc
+++ b/src/constants.cc
@@ -81,7 +81,8 @@ namespace php_arma
         );
 #endif // ARMA_USE_HDF5
         const_declare(features_ce       = abstract_class_register<features_php_name>(),
-            std::tuple("OPERATORS",       features::operators)
+            std::tuple("OPERATORS",       features::operators),
+            std::tuple("HDF5",            features::hdf5)
         );
     }
 }
diff --git a/stubs/Features.php b/stubs/Features.php
index 953dbef..ad0e61c 100644
--- a/stubs/Features.php
+++ b/stubs/Features.php
@@ -15,4 +15,9 @@ abstract class Features
      * Whether operator overloading is supported.
      */
     const OPERATORS = true;
+
+    /**
+     * Whether data can be saved into or loaded from files in HDF5 format.
+     */
+    const HDF5 = true;
 }