diff --git a/mono/metadata/ChangeLog b/mono/metadata/ChangeLog
index 6fc8020a85c53..13869a398fced 100644
--- a/mono/metadata/ChangeLog
+++ b/mono/metadata/ChangeLog
@@ -1,3 +1,7 @@
+2006-01-24  Atsushi Enomoto  <atsushi@ximian.com>
+
+	* object.c, marshal.c : Fixed runtime part of bug #77315. Reject
+	  invalid surrogate in UTF7/UTF8 bytes and don't return NULL.
 
 Tue Jan 24 09:56:16 CET 2006 Paolo Molaro <lupus@ximian.com>
 
diff --git a/mono/metadata/marshal.c b/mono/metadata/marshal.c
index 9b8476e5376df..3ab12fa164291 100644
--- a/mono/metadata/marshal.c
+++ b/mono/metadata/marshal.c
@@ -485,9 +485,9 @@ mono_string_to_lpstr (MonoString *s)
 
 	tmp = g_utf16_to_utf8 (mono_string_chars (s), s->length, NULL, &len, &error);
 	if (error) {
-		g_warning (error->message);
+		MonoException *exc = mono_get_exception_argument ("string", error->message);
 		g_error_free (error);
-		return NULL;
+		mono_raise_exception(exc);
 	}
 	else {
 		as = CoTaskMemAlloc (len + 1);
diff --git a/mono/metadata/object.c b/mono/metadata/object.c
index b222f0ac1849b..0b96e930c25bd 100644
--- a/mono/metadata/object.c
+++ b/mono/metadata/object.c
@@ -3234,8 +3234,9 @@ mono_string_to_utf8 (MonoString *s)
 
 	as = g_utf16_to_utf8 (mono_string_chars (s), s->length, NULL, NULL, &error);
 	if (error) {
-		g_warning (error->message);
+		MonoException *exc = mono_get_exception_argument ("string", error->message);
 		g_error_free (error);
+		mono_raise_exception(exc);
 	}
 
 	return as;