diff --git a/rtcore.h b/rtcore.h
index 36705ad..5114914 100644
--- a/rtcore.h
+++ b/rtcore.h
@@ -293,7 +293,7 @@ RTC_API void *
 ArenaAlloc(arena *a, isize size, isize align, isize n, int flags)
 {
 	isize padding = -(usize)a->begin & (align - 1);
-	isize available = a->end - a->begin - padding;
+	isize available = (isize)(a->end - a->begin) - padding;
 	if (available < 0 || n > available / size)
 	{
 		if (!(flags & ALLOC_SOFTFAIL))
@@ -301,7 +301,7 @@ ArenaAlloc(arena *a, isize size, isize align, isize n, int flags)
 		return NULL;
 	}
 	void *p = a->begin + padding;
-	a->begin += padding - n * size;
+	a->begin += padding + n * size;
 	return (flags & ALLOC_NOZERO) ? p : memset(p, 0, n * size);
 }