diff --git a/include/c11log/details/stack_buf.h b/include/c11log/details/stack_buf.h
index bc743349..cb45ac96 100644
--- a/include/c11log/details/stack_buf.h
+++ b/include/c11log/details/stack_buf.h
@@ -98,7 +98,7 @@ private:
             std::copy_n(other._stack_array.begin(), other._stack_size, _stack_array.begin());        
     }
 
-	bool vector_used() const
+	inline bool vector_used() const
 	{
 		return !(_v.empty());
 	}