diff --git a/runtime/compiletime/instr.c b/runtime/compiletime/instr.c
index afc72d0..6cac91f 100644
--- a/runtime/compiletime/instr.c
+++ b/runtime/compiletime/instr.c
@@ -1,7 +1,10 @@
 /* code from https://github.com/gwsystems/silverfish/blob/master/runtime/runtime.c */
 #include <assert.h>
+#include <math.h>
 #include <types.h>
 
+#define CHAR_BIT 8
+
 // TODO: Throughout here we use `assert` for error conditions, which isn't optimal
 // Instead we should use `unlikely` branches to a single trapping function (which should optimize better)
 // The below functions are for implementing WASM instructions