diff --git a/ChangeLog b/ChangeLog
index d22d422a6c..898a62131d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,7 @@
-Thu Apr 14 21:21:01 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+Thu Apr 14 21:21:06 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* include/ruby/win32.h (frexp, modf): wrongly declared as pure in
+	  mingw math.h.
 
 	* include/ruby/win32.h (ftruncate, truncate): mingw64 misses
 	  prototypes.
diff --git a/include/ruby/win32.h b/include/ruby/win32.h
index cafd7de85f..22c35e6a95 100644
--- a/include/ruby/win32.h
+++ b/include/ruby/win32.h
@@ -692,6 +692,20 @@ uintptr_t rb_w32_asynchronize(asynchronous_func_t func, uintptr_t self, int argc
 #pragma GCC visibility pop
 #endif
 
+#ifdef __MINGW_ATTRIB_PURE
+/* get rid of bugs in math.h of mingw */
+#define frexp(_X, _Y) __extension__ ({\
+    int *intptr_frexp_bug = (_Y);\
+    *intptr_frexp_bug = *intptr_frexp_bug;\
+    frexp((_X), intptr_frexp_bug);\
+})
+#define modf(_X, _Y) __extension__ ({\
+    double *intptr_modf_bug = (_Y);\
+    *intptr_modf_bug = *intptr_modf_bug;\
+    modf((_X), intptr_modf_bug);\
+})
+#endif
+
 #if defined(__cplusplus)
 #if 0
 { /* satisfy cc-mode */