diff --git a/ChangeLog b/ChangeLog
index eae337562e..4f0131cf58 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat Jul 18 09:07:00 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* random.c (fill_random_seed): use cryptographic service on Windows.
+
 Sat Jul 18 07:56:00 2009  Hidetoshi NAGAI  <nagai@ai.kyutech.ac.jp>
 
 	* ext/tk/lib/tk.rb: fail to create a widget object for an unknown
diff --git a/random.c b/random.c
index f67b65f2be..8013a51d01 100644
--- a/random.c
+++ b/random.c
@@ -389,6 +389,8 @@ fill_random_seed(unsigned int seed[DEFAULT_SEED_CNT])
 #if USE_DEV_URANDOM
     int fd;
     struct stat statbuf;
+#elif defined(_WIN32)
+    HCRYPTPROV prov;    
 #endif
 
     memset(seed, 0, DEFAULT_SEED_LEN);
@@ -410,6 +412,11 @@ fill_random_seed(unsigned int seed[DEFAULT_SEED_CNT])
         }
         close(fd);
     }
+#elif defined(_WIN32)
+    if (CryptAcquireContext(&prov, NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT)) {
+	CryptGenRandom(prov, DEFAULT_SEED_LEN, seed);
+	CryptReleaseContext(prov, 0);
+    }
 #endif
 
     gettimeofday(&tv, 0);