diff --git a/newlib/ChangeLog b/newlib/ChangeLog
index 994eee936..3f29becdb 100644
--- a/newlib/ChangeLog
+++ b/newlib/ChangeLog
@@ -1,3 +1,8 @@
+Mon Jan 29 23:03:06 2001  Christopher Faylor <cgf@cygnus.com>
+
+	* libc/stdlib/mallocr.c: Undefine windows preprocessor variables when
+	compiling under Cygwin.
+
 2001-01-29  Jeff Johnston  <jjohnstn@redhat.com>
 
 	* libc/include/math.h (signgam): Change to errno-like solution
diff --git a/newlib/libc/stdlib/mallocr.c b/newlib/libc/stdlib/mallocr.c
index c2b2fb91f..d269dd390 100644
--- a/newlib/libc/stdlib/mallocr.c
+++ b/newlib/libc/stdlib/mallocr.c
@@ -304,6 +304,11 @@ extern "C" {
 #define MALLOC_LOCK __malloc_lock(reent_ptr)
 #define MALLOC_UNLOCK __malloc_unlock(reent_ptr)
 
+#ifdef __CYGWIN__
+# undef _WIN32
+# undef WIN32
+#endif
+
 #ifndef _WIN32
 #ifdef SMALL_MEMORY
 #define malloc_getpagesize (128)