diff --git a/ChangeLog b/ChangeLog
index 4ea77e9ae2..bf6ed48bd2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2008-04-03  Michael Natterer  <mitch@gimp.org>
+
+	* app/core/gimpimage-convert.c (gimp_image_convert): don't accept
+	palettes with more than 256 colors.
+
+	* tools/pdbgen/pdb/convert.pdb: fail here too for palettes
+	with > 256 colors. Fixes bug #525471.
+
+	* app/pdb/convert_cmds.c: regenerated.
+
 2008-04-03  Jordi Mallach  <jordi@sindominio.net>
 
 	* configure.in (ALL_LINGUAS): Add Valencian-Catalan (ca@valencia).
diff --git a/app/core/gimpimage-convert.c b/app/core/gimpimage-convert.c
index 6a41daafc0..f0d0cee206 100644
--- a/app/core/gimpimage-convert.c
+++ b/app/core/gimpimage-convert.c
@@ -780,6 +780,8 @@ gimp_image_convert (GimpImage               *image,
     {
       g_return_val_if_fail (custom_palette == NULL ||
                             GIMP_IS_PALETTE (custom_palette), FALSE);
+      g_return_val_if_fail (custom_palette == NULL ||
+                            custom_palette->n_colors <= 256, FALSE);
 
       if (! custom_palette)
         palette_type = GIMP_MONO_PALETTE;
diff --git a/app/pdb/convert_cmds.c b/app/pdb/convert_cmds.c
index 4e6cc4446e..19820909ca 100644
--- a/app/pdb/convert_cmds.c
+++ b/app/pdb/convert_cmds.c
@@ -26,13 +26,17 @@
 
 #include "core/gimpimage-convert.h"
 #include "core/gimpimage.h"
+#include "core/gimppalette.h"
 #include "core/gimpparamspecs.h"
 
 #include "gimppdb.h"
+#include "gimppdberror.h"
 #include "gimppdb-utils.h"
 #include "gimpprocedure.h"
 #include "internal_procs.h"
 
+#include "gimp-intl.h"
+
 
 static GValueArray *
 image_convert_rgb_invoker (GimpProcedure      *procedure,
@@ -125,7 +129,16 @@ image_convert_indexed_invoker (GimpProcedure      *procedure,
             case GIMP_CUSTOM_PALETTE:
               pal = gimp_pdb_get_palette (gimp, palette, FALSE, error);
               if (! pal)
-                success = FALSE;
+                {
+                  success = FALSE;
+                }
+              else if (pal->n_colors > 256)
+                {
+                  g_set_error (error, GIMP_PDB_ERROR, GIMP_PDB_INVALID_ARGUMENT,
+                               _("Cannot convert to a palette "
+                                 "with more than 256 colors."));
+                  success = FALSE;
+                }
               break;
 
             default:
@@ -165,7 +178,7 @@ image_convert_set_dither_matrix_invoker (GimpProcedure      *procedure,
 
   if (success)
     {
-        gimp_image_convert_set_dither_matrix (width, height, (guchar *) matrix);
+      gimp_image_convert_set_dither_matrix (width, height, (guchar *) matrix);
     }
 
   return gimp_procedure_get_return_values (procedure, success);
diff --git a/tools/pdbgen/pdb/convert.pdb b/tools/pdbgen/pdb/convert.pdb
index 554bd09dfe..eff367b3e4 100644
--- a/tools/pdbgen/pdb/convert.pdb
+++ b/tools/pdbgen/pdb/convert.pdb
@@ -133,8 +133,17 @@ HELP
 	case GIMP_CUSTOM_PALETTE:
           pal = gimp_pdb_get_palette (gimp, palette, FALSE, error);
 	  if (! pal)
-	    success = FALSE;
-	  break;
+            {
+              success = FALSE;
+            }
+          else if (pal->n_colors > 256)
+            {
+              g_set_error (error, GIMP_PDB_ERROR, GIMP_PDB_INVALID_ARGUMENT,
+                           _("Cannot convert to a palette "
+                             "with more than 256 colors."));
+              success = FALSE;
+            }
+          break;
 
 	default:
           break;
@@ -177,7 +186,7 @@ HELP
     %invoke = (
 	code => <<'CODE'
 {
-    gimp_image_convert_set_dither_matrix (width, height, (guchar *) matrix);
+  gimp_image_convert_set_dither_matrix (width, height, (guchar *) matrix);
 }
 CODE
     );
@@ -185,7 +194,10 @@ CODE
 
 @headers = qw("core/gimpimage.h"
               "core/gimpimage-convert.h"
-              "gimppdb-utils.h");
+              "core/gimppalette.h"
+              "gimppdberror.h"
+              "gimppdb-utils.h"
+              "gimp-intl.h");
 
 @procs = qw(image_convert_rgb
             image_convert_grayscale