diff --git a/portable.h b/portable.h
index fb76db90..c5905ccf 100644
--- a/portable.h
+++ b/portable.h
@@ -31,6 +31,13 @@
 #include <windows.h>
 #endif
 
+/**
+ * Compiler extension
+ */
+#ifndef __always_inline
+#define __always_inline inline __attribute__((always_inline))
+#endif
+
 /**
  * Architecture.
  */