diff --git a/ChangeLog b/ChangeLog
index 95d3a3df6d..5c14731632 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Sep  6 13:56:14 2001  Akinori MUSHA  <knu@iDaemons.org>
+
+	* ext/digest/digest.c (rb_digest_base_s_digest,
+	  rb_digest_base_s_hexdigest): ensure that a string is given.
+
 Thu Sep  6 13:28:51 2001  WATANABE Hirofumi  <eban@ruby-lang.org>
 
 	* lib/jcode.rb (_regexp_quote): fix quote handling, again.
diff --git a/ext/digest/digest.c b/ext/digest/digest.c
index f737d254ab..5355776119 100644
--- a/ext/digest/digest.c
+++ b/ext/digest/digest.c
@@ -96,6 +96,12 @@ rb_digest_base_s_digest(class, str)
     if (class == cDigest_Base)
 	rb_raise(rb_eNotImpError, "Digest::Base is an abstract class");
 
+#ifdef StringValue
+    StringValue(str);
+#else
+    Check_Type(str, T_STRING);
+#endif
+
     algo = get_digest_base_metadata(class);
 
     pctx = xmalloc(algo->ctx_size);
@@ -129,6 +135,12 @@ rb_digest_base_s_hexdigest(class, str)
     if (class == cDigest_Base)
 	rb_raise(rb_eNotImpError, "Digest::Base is an abstract class");
 
+#ifdef StringValue
+    StringValue(str);
+#else
+    Check_Type(str, T_STRING);
+#endif
+
     algo = get_digest_base_metadata(class);
 
     pctx = xmalloc(algo->ctx_size);