diff --git a/include/stddef.h b/include/stddef.h
index 791ba31..31b60dd 100644
--- a/include/stddef.h
+++ b/include/stddef.h
@@ -8,8 +8,9 @@ typedef __PTRDIFF_TYPE__ ptrdiff_t;
 typedef __PTRDIFF_TYPE__ intptr_t;
 typedef __SIZE_TYPE__ uintptr_t;
 
-#ifndef __int8_t_defined
+#if !defined(__int8_t_defined) && !defined(___int8_t_defined)
 #define __int8_t_defined
+#define ___int8_t_defined
 typedef signed char int8_t;
 typedef signed short int int16_t;
 typedef signed int int32_t;
diff --git a/lib/bcheck.c b/lib/bcheck.c
index 18415cd..e3a8ef2 100644
--- a/lib/bcheck.c
+++ b/lib/bcheck.c
@@ -17,10 +17,10 @@
  * License along with this library; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  */
-#include <stddef.h>
 #include <stdio.h>
 #include <stdarg.h>
 #include <string.h>
+#include <stddef.h>
 #if !defined(__FreeBSD__) && !defined(__FreeBSD_kernel__) \
     && !defined(__DragonFly__) && !defined(__OpenBSD__) && !defined(__NetBSD__)
 #include <malloc.h>
@@ -47,7 +47,7 @@ extern void *sbrk (intptr_t __delta);
 #if defined(__FreeBSD__) || defined(__FreeBSD_kernel__) \
     || defined(__DragonFly__) || defined(__dietlibc__) \
     || defined(__UCLIBC__) || defined(__OpenBSD__) || defined(__NetBSD__) \
-    || defined(_WIN32) || defined(TCC_UCLIBC)
+    || defined(_WIN32) || defined(TCC_UCLIBC) || defined(__CYGWIN__)
 #warning Bound checking does not support malloc (etc.) in this environment.
 #undef CONFIG_TCC_MALLOC_HOOKS
 #undef HAVE_MEMALIGN
diff --git a/libtcc.c b/libtcc.c
index 7d9a058..a5ec7f3 100644
--- a/libtcc.c
+++ b/libtcc.c
@@ -1170,6 +1170,8 @@ LIBTCCAPI TCCState *tcc_new(void)
 # ifdef TCC_TARGET_X86_64
     tcc_define_symbol(s, "_WIN64", NULL);
 # endif
+#elif defined(__CYGWIN__)
+    tcc_define_symbol(s, "__CYGWIN__", NULL);
 #else
     tcc_define_symbol(s, "__unix__", NULL);
     tcc_define_symbol(s, "__unix", NULL);
diff --git a/tccrun.c b/tccrun.c
index 52d3015..72c62e9 100644
--- a/tccrun.c
+++ b/tccrun.c
@@ -502,7 +502,7 @@ static int rt_get_caller_pc(addr_t *paddr, ucontext_t *uc, int level)
         *paddr = uc->uc_mcontext->__ss.__eip;
 #elif defined(__FreeBSD__) || defined(__FreeBSD_kernel__) || defined(__DragonFly__)
         *paddr = uc->uc_mcontext.mc_eip;
-#elif defined(__dietlibc__)
+#elif defined(__dietlibc__) || defined(__CYGWIN__)
         *paddr = uc->uc_mcontext.eip;
 #elif defined(__NetBSD__)
         *paddr = uc->uc_mcontext.__gregs[_REG_EIP];
@@ -515,7 +515,7 @@ static int rt_get_caller_pc(addr_t *paddr, ucontext_t *uc, int level)
         fp = uc->uc_mcontext->__ss.__ebp;
 #elif defined(__FreeBSD__) || defined(__FreeBSD_kernel__) || defined(__DragonFly__)
         fp = uc->uc_mcontext.mc_ebp;
-#elif defined(__dietlibc__)
+#elif defined(__dietlibc__) || defined(__CYGWIN__)
         fp = uc->uc_mcontext.ebp;
 #elif defined(__NetBSD__)
         fp = uc->uc_mcontext.__gregs[_REG_EBP];