diff --git a/.travis.yml b/.travis.yml
index 15b2b77..ebe88d1 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,6 +9,8 @@ stages:
   - Test CommonMark (weak)
 
 php:
+  - 5.5
+  - 5.6
   - 7.0
   - 7.1
   - 7.2
diff --git a/src/Configurable.php b/src/Configurable.php
index 191ec1a..eaccce0 100644
--- a/src/Configurable.php
+++ b/src/Configurable.php
@@ -5,5 +5,5 @@ namespace Erusev\Parsedown;
 interface Configurable
 {
     /** @return static */
-    public static function default();
+    public static function initial();
 }
diff --git a/src/Configurables/DefinitionBook.php b/src/Configurables/DefinitionBook.php
index 0e73db5..0c22538 100644
--- a/src/Configurables/DefinitionBook.php
+++ b/src/Configurables/DefinitionBook.php
@@ -21,7 +21,7 @@ final class DefinitionBook implements Configurable
     }
 
     /** @return self */
-    public static function default()
+    public static function initial()
     {
         return new self;
     }
diff --git a/src/Configurables/SafeMode.php b/src/Configurables/SafeMode.php
index e746027..bcb8e4b 100644
--- a/src/Configurables/SafeMode.php
+++ b/src/Configurables/SafeMode.php
@@ -22,7 +22,7 @@ final class SafeMode implements Configurable
         return $this->enabled;
     }
 
-    public static function default(): self
+    public static function initial(): self
     {
         return new self(false);
     }
diff --git a/src/Configurables/StrictMode.php b/src/Configurables/StrictMode.php
index 380a9bf..a460d31 100644
--- a/src/Configurables/StrictMode.php
+++ b/src/Configurables/StrictMode.php
@@ -22,7 +22,7 @@ final class StrictMode implements Configurable
         return $this->enabled;
     }
 
-    public static function default(): self
+    public static function initial(): self
     {
         return new self(false);
     }
diff --git a/src/State.php b/src/State.php
index 8d55eb5..aec242f 100644
--- a/src/State.php
+++ b/src/State.php
@@ -67,7 +67,7 @@ final class State
     {
         return (isset($this->state[$configurableClass])
             ? $this->state[$configurableClass]
-            : $configurableClass::default()
+            : $configurableClass::initial()
         );
     }