diff --git a/ChangeLog b/ChangeLog
index 0395297f4..adaba1ca1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,21 @@
+2006-06-08  suzuki toshiya  <mpsuzuki@hiroshima-u.ac.jp>
+
+	Public API of TrueTypeGX, OpenType and classic kern table validator
+	should return FT_Err_Unimplemented_Feature, when validation service
+	is unavailable (disabled by modules.cfg). It is originally suggested
+	by David Turner:
+	http://lists.gnu.org/archive/html/freetype-devel/2005-11/msg00078.html
+
+	* src/base/ftgxval.c (FT_TrueTypeGX_Validate): return
+	FT_Err_Unimplemented_Feature, When TrueTypeGX validation service
+	is unavailable.
+	(FT_ClassicKern_Validate): return FT_Err_Unimplemented_Feature,
+	when classic kern table validation service is unavailable.
+
+	* src/base/ftotval.c (FT_OpenType_Validate): return
+	FT_Err_Unimplemented_Feature, When OpenType validation service
+	is unavailable.
+
 2006-06-08  Werner Lemberg  <wl@gnu.org>
 
 	* src/bdf/bdflib.c (bdf_load_font): Fix memory leaks in case of
diff --git a/src/base/ftgxval.c b/src/base/ftgxval.c
index 615e5ed6f..687bf5001 100644
--- a/src/base/ftgxval.c
+++ b/src/base/ftgxval.c
@@ -62,7 +62,7 @@
                                  tables,
                                  table_length );
     else
-      error = FT_Err_Invalid_Argument;
+      error = FT_Err_Unimplemented_Feature;
 
   Exit:
     return error;
@@ -108,7 +108,7 @@
                                  validation_flags,
                                  ckern_table );
     else
-      error = FT_Err_Invalid_Argument;
+      error = FT_Err_Unimplemented_Feature;
 
   Exit:
     return error;
diff --git a/src/base/ftotval.c b/src/base/ftotval.c
index f14580d29..20f21fa3f 100644
--- a/src/base/ftotval.c
+++ b/src/base/ftotval.c
@@ -62,7 +62,7 @@
                                  GSUB_table,
                                  JSTF_table );
     else
-      error = FT_Err_Invalid_Argument;
+      error = FT_Err_Unimplemented_Feature;
 
   Exit:
     return error;