diff --git a/Makefile b/Makefile
index 79d6aae4..ac5e7c9b 100644
--- a/Makefile
+++ b/Makefile
@@ -36,10 +36,16 @@ PLATFORM=mingw
 SOLIBDIR = $(BINDIR)
 DIFFOPTS = -b
 else
+ifeq ($(shell uname -o),Cygwin)
+PLATFORM=cygwin
+SOLIBDIR = $(BINDIR)
+DIFFOPTS = -b
+else
 PLATFORM=unix
 endif
 endif
 endif
+endif
 
 ifeq ($(PLATFORM),macosx)
 SO  = .dylib
@@ -57,12 +63,20 @@ LDFLAGS += -Wl,--out-implib,libchibi-scheme$(SO).a
 STATICFLAGS = -DSEXP_USE_DL=0
 LIBDL = 
 else
+ifeq ($(PLATFORM),cygwin)
+SO  = .dll
+EXE = .exe
+CC = gcc
+CLIBFLAGS = -shared
+LDFLAGS += -Wl,--out-implib,libchibi-scheme$(SO).a
+else
 SO  = .so
 EXE =
 CLIBFLAGS = -fPIC -shared
 STATICFLAGS = -static -DSEXP_USE_DL=0
 endif
 endif
+endif
 
 ifeq ($(USE_BOEHM),1)
 SEXP_USE_BOEHM = 1
diff --git a/include/chibi/sexp.h b/include/chibi/sexp.h
index dd3de98d..39a3ea58 100644
--- a/include/chibi/sexp.h
+++ b/include/chibi/sexp.h
@@ -129,6 +129,11 @@ typedef unsigned int sexp_tag_t;
 typedef unsigned long sexp_uint_t;
 typedef long sexp_sint_t;
 #define sexp_heap_align(n) sexp_align(n, 5)
+#elif __CYGWIN__
+typedef unsigned short sexp_tag_t;
+typedef unsigned int sexp_uint_t;
+typedef int sexp_sint_t;
+#define sexp_heap_align(n) sexp_align(n, 5)
 #else
 typedef unsigned short sexp_tag_t;
 typedef unsigned int sexp_uint_t;
diff --git a/lib/srfi/69/hash.c b/lib/srfi/69/hash.c
index e739ff1c..42d1e864 100644
--- a/lib/srfi/69/hash.c
+++ b/lib/srfi/69/hash.c
@@ -34,7 +34,7 @@ static sexp sexp_string_hash (sexp ctx sexp_api_params(self, n), sexp str, sexp
 
 static sexp_uint_t string_ci_hash (char *str, sexp_uint_t bound) {
   sexp_uint_t acc = FNV_OFFSET_BASIS;
-  while (*str) {acc *= FNV_PRIME; acc ^= tolower(*str++);}
+  while (*str) {acc *= FNV_PRIME; acc ^= (tolower)(*str++);}
   return acc % bound;
 }
 
diff --git a/main.c b/main.c
index 03caf762..d07a9767 100644
--- a/main.c
+++ b/main.c
@@ -163,8 +163,8 @@ void run_main (int argc, char **argv) {
       check_nonull_arg('h', arg);
       heap_size = atol(arg);
       len = strlen(arg);
-      if (heap_size && isalpha(arg[len-1])) {
-        switch (tolower(arg[len-1])) {
+      if (heap_size && (isalpha)(arg[len-1])) {
+        switch ((tolower)(arg[len-1])) {
         case 'k': heap_size *= 1024; break;
         case 'm': heap_size *= (1024*1024); break;
         }
diff --git a/sexp.c b/sexp.c
index 5f38669a..8a6f0079 100644
--- a/sexp.c
+++ b/sexp.c
@@ -1659,7 +1659,7 @@ sexp sexp_read_raw (sexp ctx, sexp in) {
         if (sexp_string_length(res) == 1) {
           res = sexp_make_character(c1);
         } else if ((c1 == 'x' || c1 == 'X') &&
-                   isxdigit(str[1]) && isxdigit(str[2]) && str[3] == '\0') {
+                   (isxdigit)(str[1]) && (isxdigit)(str[2]) && str[3] == '\0') {
           res = sexp_make_character(16 * digit_value(str[1])
                                     + digit_value(str[2]));
         } else {