diff --git a/ringbuf.c b/ringbuf.c
index 23adb94..9ea1a6d 100644
--- a/ringbuf.c
+++ b/ringbuf.c
@@ -40,9 +40,9 @@ rb_init(struct RingBuf *rb, rb_size_t capacity, ALLOC_T malloc_fn,
 }
 
 void
-rb_destroy(struct RingBuf *rb, void(free)())
+rb_destroy(struct RingBuf *rb, FREE_T free_fn)
 {
-  free(rb->buffer);
+  free_fn(rb->buffer);
 }
 
 void
diff --git a/ringbuf.h b/ringbuf.h
index 4e3cbb8..6d6d01f 100644
--- a/ringbuf.h
+++ b/ringbuf.h
@@ -12,6 +12,9 @@ typedef void *(*ALLOC_T)(rb_size_t);
 /** Signature of memcpy */
 typedef void *(*MEMCPY_T)(void *, const void *, rb_size_t);
 
+/** Signature of free */
+typedef void (*FREE_T)(void *);
+
 /**
  * @brief Ring buffer, also known as circular buffer.
  */