--- a/c/scheme48vm-prelude.h
+++ b/c/scheme48vm-prelude.h
@@ -5,7 +5,7 @@
 #include "c-mods.h"
 #include "write-barrier.h"
 
-#define SMALL_MULTIPLY(x,y) ((x) * (y))
+#define SMALL_MULTIPLY(x,y) ((long)((unsigned long)(x) * (unsigned long)(y)))
 
 #define	NO_ERRORS	0		/* extension to errno.h */