diff --git a/include/chibi/sexp.h b/include/chibi/sexp.h
index 7a8c9a77..f82f2225 100644
--- a/include/chibi/sexp.h
+++ b/include/chibi/sexp.h
@@ -20,11 +20,11 @@ extern "C" {
 #ifdef _WIN32
 #include <windows.h>
 #include <errno.h>
-#define sexp_isalpha(x) ((isalpha)((int)(x)))
-#define sexp_isxdigit(x) ((isxdigit)((int)(x)))
-#define sexp_isdigit(x) ((isdigit)((int)(x)))
-#define sexp_tolower(x) ((tolower)((int)(x)))
-#define sexp_toupper(x) ((toupper)((int)(x)))
+#define sexp_isalpha(x) (isalpha(x))
+#define sexp_isxdigit(x) (isxdigit(x))
+#define sexp_isdigit(x) (isdigit(x))
+#define sexp_tolower(x) (tolower(x))
+#define sexp_toupper(x) (toupper(x))
 #define SEXP_USE_POLL_PORT 0
 #define sexp_poll_input(ctx, port) usleep(SEXP_POLL_SLEEP_TIME)
 #define sexp_poll_output(ctx, port) usleep(SEXP_POLL_SLEEP_TIME)
diff --git a/lib/srfi/151/bit.c b/lib/srfi/151/bit.c
index f5fb306a..57f469fe 100644
--- a/lib/srfi/151/bit.c
+++ b/lib/srfi/151/bit.c
@@ -398,13 +398,13 @@ sexp sexp_bit_set_p (sexp ctx, sexp self, sexp_sint_t n, sexp i, sexp x) {
     return sexp_xtype_exception(ctx, self, "index must be non-negative", i);
   if (sexp_fixnump(x)) {
     return sexp_make_boolean((pos < sizeof(sexp_uint_t)*CHAR_BIT)
-                             && (sexp_unbox_fixnum(x) & (1UL<<pos)));
+                             && (sexp_unbox_fixnum(x) & ((sexp_uint_t)1<<pos)));
 #if SEXP_USE_BIGNUMS
   } else if (sexp_bignump(x)) {
     pos /= (sizeof(sexp_uint_t)*CHAR_BIT);
     rem = (sexp_unbox_fixnum(i) - pos*sizeof(sexp_uint_t)*CHAR_BIT);
     return sexp_make_boolean((pos < (sexp_sint_t)sexp_bignum_length(x))
-                             && (sexp_bignum_data(x)[pos] & (1UL<<rem)));
+                             && (sexp_bignum_data(x)[pos] & ((sexp_uint_t)1<<rem)));
 #endif
   } else {
     return sexp_type_exception(ctx, self, SEXP_FIXNUM, x);