diff --git a/src/arena_allocator.h b/src/arena_allocator.h
index 7bb99aa..981f76c 100644
--- a/src/arena_allocator.h
+++ b/src/arena_allocator.h
@@ -5,7 +5,7 @@
 typedef struct {
   size_t capacity;
   size_t size;
-  char *data;
+  unsigned char *data;
 } Arena;
 
 Arena arena_init(size_t capacity);