diff --git a/src/core/Span.h b/src/core/Span.h
index 586d600..b3d1829 100644
--- a/src/core/Span.h
+++ b/src/core/Span.h
@@ -2,13 +2,14 @@
 #define SPAN_H
 
 #include <stdint.h>
+#include <stdlib.h>
 
 struct Span
 {
     uint8_t * start;
-    uint32_t length;
+    size_t length;
 
-    Span(uint8_t * _start, uint32_t _length)
+    Span(uint8_t * _start, size_t _length)
         : start(_start),
           length(_length)
     {