diff --git a/gc.c b/gc.c
index d1a9174fae..17627dacd8 100644
--- a/gc.c
+++ b/gc.c
@@ -10389,7 +10389,7 @@ rb_aligned_malloc(size_t alignment, size_t size)
 #elif defined _WIN32
     void *_aligned_malloc(size_t, size_t);
     res = _aligned_malloc(size, alignment);
-#elif defined(HAVE_MMAP)
+#elif defined(HAVE_MMAP) && !defined(__CYGWIN__)
     GC_ASSERT(alignment % sysconf(_SC_PAGE_SIZE) == 0);

     char *ptr = mmap(NULL, alignment + size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
@@ -10441,7 +10441,7 @@ rb_aligned_free(void *ptr, size_t size)
     __mingw_aligned_free(ptr);
 #elif defined _WIN32
     _aligned_free(ptr);
-#elif defined HAVE_MMAP
+#elif defined HAVE_MMAP && !defined(__CYGWIN__)
     GC_ASSERT(size % sysconf(_SC_PAGE_SIZE) == 0);
     if (munmap(ptr, size)) {
         rb_bug("rb_aligned_free: munmap failed");