diff --git a/libvips/include/vips/debug.h b/libvips/include/vips/debug.h
index 808edbf9..14fdea21 100644
--- a/libvips/include/vips/debug.h
+++ b/libvips/include/vips/debug.h
@@ -66,9 +66,6 @@ extern "C" {
 	G_STMT_START { ; } G_STMT_END
 #endif /*VIPS_DEBUG_GREEN*/
 
-int im_image_sanity( VipsImage *im );
-void im_image_sanity_all( void );
-
 #ifdef __cplusplus
 }
 #endif /*__cplusplus*/
diff --git a/libvips/include/vips/internal.h b/libvips/include/vips/internal.h
index e1ea346b..07f8a31e 100644
--- a/libvips/include/vips/internal.h
+++ b/libvips/include/vips/internal.h
@@ -196,8 +196,6 @@ int im__munmap( void *start, size_t length );
 int im__write( int, const void *, size_t );
 void im__change_suffix( const char *name, char *out, int mx,
         const char *new_suff, const char **olds, int nolds );
-void im__print_all( void );
-void im__print_one( int );
 int im__trigger_callbacks( GSList *cblist );
 int im__close( VipsImage * );
 int im__fft_sp( float *rvec, float *ivec, int logrows, int logcols );
diff --git a/libvips/include/vips/object.h b/libvips/include/vips/object.h
index 2d1f22f3..949970ab 100644
--- a/libvips/include/vips/object.h
+++ b/libvips/include/vips/object.h
@@ -212,6 +212,11 @@ struct _VipsObjectClass {
 	 */
 	void (*print)( VipsObject *, VipsBuf * );
 
+	/* Sanity-check the object. Print messages and stuff. 
+	 * Handy for debugging.
+	 */
+	void (*sanity)( VipsObject *, VipsBuf * );
+
 	/* Just before close, everything is still alive.
 	 */
 	void (*preclose)( VipsObject * );
@@ -252,6 +257,7 @@ void vips_object_preclose( VipsObject *object );
 int vips_object_build( VipsObject *object );
 void vips_object_print_class( VipsObjectClass *klass );
 void vips_object_print( VipsObject *object );
+gboolean vips_object_sanity( VipsObject *object );
 
 GType vips_object_get_type( void );
 
@@ -283,6 +289,9 @@ void vips_object_local_cb( VipsObject *vobject, GObject *gobject );
 	g_signal_connect( V, "close", \
 		G_CALLBACK( vips_object_local_cb ), G );
 
+void vips_object_print_all( void );
+void vips_object_sanity_all( void );
+
 #ifdef __cplusplus
 }
 #endif /*__cplusplus*/
diff --git a/libvips/include/vips/vips7compat.h b/libvips/include/vips/vips7compat.h
index e73194b7..a35a8663 100644
--- a/libvips/include/vips/vips7compat.h
+++ b/libvips/include/vips/vips7compat.h
@@ -189,6 +189,10 @@ extern "C" {
 
 #define im__region_no_ownership vips__region_no_ownership
 
+#define im_image_sanity( I ) (!vips_object_sanity( VIPS_OBJECT( I ) ))
+#define im_image_sanity_all vips_object_sanity_all
+#define im__print_all vips_object_print_all
+
 /* Compat functions.
  */
 
diff --git a/libvips/iofuncs/Makefile.am b/libvips/iofuncs/Makefile.am
index 988c2e30..528f5034 100644
--- a/libvips/iofuncs/Makefile.am
+++ b/libvips/iofuncs/Makefile.am
@@ -6,7 +6,6 @@ libiofuncs_la_SOURCES = \
 	meta.c \
 	base64.h \
 	base64.c \
-	debug.c \
 	dispatch_types.c \
 	error.c \
 	image.c \
diff --git a/libvips/iofuncs/check.c b/libvips/iofuncs/check.c
index a6ee2a48..8027d2a8 100644
--- a/libvips/iofuncs/check.c
+++ b/libvips/iofuncs/check.c
@@ -175,7 +175,7 @@ convert_otom( IMAGE *im )
 int
 im_incheck( IMAGE *im )
 {	
-	g_assert( !im_image_sanity( im ) );
+	g_assert( vips_object_sanity( VIPS_OBJECT( im ) ) );
 
 #ifdef DEBUG_IO
 	printf( "im_incheck: old-style input for %s\n", im->filename );
@@ -407,7 +407,7 @@ im_rwcheck( IMAGE *im )
 int
 im_pincheck( IMAGE *im )
 {	
-	g_assert( !im_image_sanity( im ) );
+	g_assert( vips_object_sanity( VIPS_OBJECT( im ) ) );
 
 #ifdef DEBUG_IO
 	printf( "im_pincheck: enabling partial input for %s\n", im->filename );
diff --git a/libvips/iofuncs/debug.c b/libvips/iofuncs/debug.c
deleted file mode 100644
index 2bd066e2..00000000
--- a/libvips/iofuncs/debug.c
+++ /dev/null
@@ -1,73 +0,0 @@
-/* debug.c: support for debugging
- *
- * 24/10/95 JC
- *	- first version
- * 24/2/05
- *	- print more mem allocation info
- * 2/10/09
- * 	- im_image_sanity() moved here
- * 	- im_printdesc() moved here
- * 5/3/11
- * 	- vips8 rewrite
- */
-
-/*
-
-    This file is part of VIPS.
-    
-    VIPS is free software; you can redistribute it and/or modify
-    it under the terms of the GNU Lesser General Public License as published by
-    the Free Software Foundation; either version 2 of the License, or
-    (at your option) any later version.
-
-    This program is distributed in the hope that it will be useful,
-    but WITHOUT ANY WARRANTY; without even the implied warranty of
-    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-    GNU Lesser General Public License for more details.
-
-    You should have received a copy of the GNU Lesser General Public License
-    along with this program; if not, write to the Free Software
-    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
-
- */
-
-/*
-
-    These files are distributed with VIPS - http://www.vips.ecs.soton.ac.uk
-
- */
-
-#ifdef HAVE_CONFIG_H
-#include <config.h>
-#endif /*HAVE_CONFIG_H*/
-#include <vips/intl.h>
-
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-
-#include <vips/vips.h>
-#include <vips/util.h>
-
-#ifdef WITH_DMALLOC
-#include <dmalloc.h>
-#endif /*WITH_DMALLOC*/
-
-/* Print something about all current objects.
- */
-void
-im__print_all( void )
-{
-	vips_object_map( (VSListMap2Fn) vips_object_print, NULL, NULL );
-}
-
-int 
-im_image_sanity( IMAGE *im )
-{
-	return( 0 );
-}
-
-void
-im_image_sanity_all( void )
-{
-}
diff --git a/libvips/iofuncs/im_generate.c b/libvips/iofuncs/im_generate.c
index 7745ed1f..76075065 100644
--- a/libvips/iofuncs/im_generate.c
+++ b/libvips/iofuncs/im_generate.c
@@ -362,7 +362,7 @@ im_generate( IMAGE *im,
 {
         int res;
 
-	g_assert( !im_image_sanity( im ) );
+	g_assert( vips_object_sanity( VIPS_OBJECT( im ) ) );
 
 	if( !im->hint_set ) {
 		vips_error( "im_generate", 
diff --git a/libvips/iofuncs/im_histlin.c b/libvips/iofuncs/im_histlin.c
index b108e5bf..2184e869 100644
--- a/libvips/iofuncs/im_histlin.c
+++ b/libvips/iofuncs/im_histlin.c
@@ -150,9 +150,8 @@ im_updatehist( IMAGE *out, const char *name, int argc, char *argv[] )
 {	
 	int i;
 	char txt[IM_MAX_LINE];
-	VipsBuf buf;
+	VipsBuf buf = VIPS_BUF_STATIC( txt );
 
-	vips_buf_init_static( &buf, txt, IM_MAX_LINE );
 	vips_buf_appends( &buf, name );
 
 	for( i = 0; i < argc; i++ ) {
diff --git a/libvips/iofuncs/im_setupout.c b/libvips/iofuncs/im_setupout.c
index fe250402..90034f08 100644
--- a/libvips/iofuncs/im_setupout.c
+++ b/libvips/iofuncs/im_setupout.c
@@ -88,7 +88,7 @@
 int
 im_setupout( IMAGE *im )
 {	
-	g_assert( !im_image_sanity( im ) );
+	g_assert( vips_object_sanity( VIPS_OBJECT( im ) ) );
 
 	if( im->Xsize <= 0 || im->Ysize <= 0 || im->Bands <= 0 ) {
 		vips_error( "im_setupout", 
diff --git a/libvips/iofuncs/image.c b/libvips/iofuncs/image.c
index e2becca0..40ed606f 100644
--- a/libvips/iofuncs/image.c
+++ b/libvips/iofuncs/image.c
@@ -31,8 +31,8 @@
  */
 
 /*
- */
 #define VIPS_DEBUG
+ */
 
 #ifdef HAVE_CONFIG_H
 #include <config.h>
@@ -448,6 +448,64 @@ vips_image_print( VipsObject *object, VipsBuf *buf )
 	VIPS_OBJECT_CLASS( vips_image_parent_class )->print( object, buf );
 }
 
+static void *
+vips_image_sanity_upstream( VipsImage *im_up, VipsImage *im_down )
+{
+	if( !g_slist_find( im_up->downstream, im_down ) ||
+		!g_slist_find( im_down->upstream, im_up ) )
+		return( im_up );
+
+	return( NULL );
+}
+
+static void *
+vips_image_sanity_downstream( VipsImage *im_down, VipsImage *im_up )
+{
+	return( vips_image_sanity_upstream( im_up, im_down ) );
+}
+
+static void
+vips_image_sanity( VipsObject *object, VipsBuf *buf )
+{
+	VipsImage *image = VIPS_IMAGE( object );
+
+	if( !image->filename ) 
+		vips_buf_appends( buf, "NULL filename\n" );
+
+	/* All -1 means im has been inited but never used.
+	 */
+	if( image->Xsize != -1 ||
+		image->Ysize != -1 ||
+		image->Bands != -1 ||
+		image->BandFmt != -1 ) {
+		if( image->Xsize <= 0 || 
+			image->Ysize <= 0 || 
+			image->Bands <= 0 ) 
+			vips_buf_appends( buf, "bad dimensions\n" );
+		if( image->BandFmt < -1 || 
+			image->BandFmt > VIPS_FORMAT_DPCOMPLEX ||
+			(image->Coding != -1 &&
+				image->Coding != VIPS_CODING_NONE && 
+				image->Coding != VIPS_CODING_LABQ &&
+				image->Coding != VIPS_CODING_RAD) ||
+			image->Type > VIPS_INTERPRETATION_GREY16 ||
+			image->dtype > VIPS_IMAGE_PARTIAL || 
+			image->dhint > VIPS_DEMAND_STYLE_ANY ) 
+			vips_buf_appends( buf, "bad enum\n" );
+		if( image->Xres < 0 || image->Xres < 0 ) 
+			vips_buf_appends( buf, "bad resolution\n" );
+	}
+
+	if( im_slist_map2( image->upstream, 
+		(VSListMap2Fn) vips_image_sanity_upstream, image, NULL ) )
+		vips_buf_appends( buf, "upstream broken\n" );
+	if( im_slist_map2( image->downstream, 
+		(VSListMap2Fn) vips_image_sanity_downstream, image, NULL ) )
+		vips_buf_appends( buf, "downstream broken\n" );
+
+	VIPS_OBJECT_CLASS( vips_image_parent_class )->sanity( object, buf );
+}
+
 static gboolean
 vips_format_is_vips( VipsFormatClass *format )
 {
@@ -983,6 +1041,7 @@ vips_image_class_init( VipsImageClass *class )
 	vobject_class->description = _( "VIPS image class" );
 
 	vobject_class->print = vips_image_print;
+	vobject_class->sanity = vips_image_sanity;
 	vobject_class->build = vips_image_build;
 
 	class->invalidate = vips_image_real_invalidate;
@@ -1286,7 +1345,8 @@ vips_image_preeval( VipsImage *image )
 		vips_object_print( VIPS_OBJECT( image ) );
 #endif /*VIPS_DEBUG*/
 
-		g_assert( !im_image_sanity( image->progress ) );
+		g_assert( vips_object_sanity( 
+			VIPS_OBJECT( image->progress ) ) );
 
 		(void) vips_progress_add( image->progress );
 
@@ -1309,7 +1369,8 @@ vips_image_eval( VipsImage *image, int w, int h )
 		vips_object_print( VIPS_OBJECT( image ) );
 #endif /*VIPS_DEBUG*/
 
-		g_assert( !im_image_sanity( image->progress ) );
+		g_assert( vips_object_sanity( 
+			VIPS_OBJECT( image->progress ) ) );
 
 		progress->run = g_timer_elapsed( progress->start, NULL );
 		progress->npels += w * h;
@@ -1333,7 +1394,8 @@ vips_image_posteval( VipsImage *image )
 		vips_object_print( VIPS_OBJECT( image ) );
 #endif /*VIPS_DEBUG*/
 
-		g_assert( !im_image_sanity( image->progress ) );
+		g_assert( vips_object_sanity( 
+			VIPS_OBJECT( image->progress ) ) );
 
 		g_signal_emit( image->progress, 
 			vips_image_signals[SIG_POSTEVAL], 0, image->time );
diff --git a/libvips/iofuncs/object.c b/libvips/iofuncs/object.c
index 994f8a8c..dc6dd8f3 100644
--- a/libvips/iofuncs/object.c
+++ b/libvips/iofuncs/object.c
@@ -30,10 +30,10 @@
  */
 
 /*
- */
 #define DEBUG
 #define VIPS_DEBUG
 #define DEBUG_REF
+ */
 
 #ifdef HAVE_CONFIG_H
 #include <config.h>
@@ -136,10 +136,9 @@ vips_object_build( VipsObject *object )
 void
 vips_object_print_class( VipsObjectClass *class )
 {
-	VipsBuf buf;
 	char str[1000];
+	VipsBuf buf = VIPS_BUF_STATIC( str );
 
-	vips_buf_init_static( &buf, str, 1000 );
 	class->print_class( class, &buf );
 	printf( "%s\n", vips_buf_all( &buf ) );
 }
@@ -148,15 +147,31 @@ void
 vips_object_print( VipsObject *object )
 {
 	VipsObjectClass *class = VIPS_OBJECT_GET_CLASS( object );
-	VipsBuf buf;
 	char str[1000];
+	VipsBuf buf = VIPS_BUF_STATIC( str );
 
 	vips_object_print_class( class );
-	vips_buf_init_static( &buf, str, 1000 );
 	class->print( object, &buf );
 	printf( "%s\n", vips_buf_all( &buf ) );
 }
 
+gboolean
+vips_object_sanity( VipsObject *object )
+{
+	VipsObjectClass *class = VIPS_OBJECT_GET_CLASS( object );
+	char str[1000];
+	VipsBuf buf = VIPS_BUF_STATIC( str );
+
+	class->sanity( object, &buf );
+	if( !vips_buf_is_empty( &buf ) ) {
+		printf( "sanity failure: " );
+		vips_object_print( object );
+		printf( "%s\n", vips_buf_all( &buf ) );
+	}
+
+	return( TRUE );
+}
+
 /* Extra stuff we track for properties to do our argument handling.
  */
 
@@ -772,6 +787,11 @@ vips_object_real_print( VipsObject *object, VipsBuf *buf )
 	vips_buf_appendf( buf, " (%p)", object );
 }
 
+static void
+vips_object_real_sanity( VipsObject *object, VipsBuf *buf )
+{
+}
+
 static void
 transform_string_double( const GValue *src_value, GValue *dest_value )
 {
@@ -798,6 +818,7 @@ vips_object_class_init( VipsObjectClass *class )
 	class->build = vips_object_real_build;
 	class->print_class = vips_object_real_print_class;
 	class->print = vips_object_real_print;
+	class->sanity = vips_object_real_sanity;
 	class->nickname = "object";
 	class->description = _( "VIPS base class" );
 
@@ -1195,3 +1216,31 @@ vips_object_unref( VipsObject *obj )
 
 	return( 0 );
 }
+
+static void *
+vips_object_print_all_cb( VipsObject *object )
+{
+	vips_object_print( object );
+
+	return( NULL );
+}
+
+void
+vips_object_print_all( void )
+{
+	vips_object_map( (VSListMap2Fn) vips_object_print_all_cb, NULL, NULL );
+}
+
+static void *
+vips_object_sanity_all_cb( VipsObject *object )
+{
+	(void) vips_object_sanity( object );
+
+	return( NULL );
+}
+
+void
+vips_object_sanity_all( void )
+{
+	vips_object_map( (VSListMap2Fn) vips_object_sanity_all_cb, NULL, NULL );
+}
diff --git a/libvips/iofuncs/region.c b/libvips/iofuncs/region.c
index b02f2089..ea383967 100644
--- a/libvips/iofuncs/region.c
+++ b/libvips/iofuncs/region.c
@@ -70,11 +70,11 @@
  */
 
 /*
- */
 #define DEBUG_MOVE 
 #define DEBUG_ENVIRONMENT 1
 #define DEBUG_CREATE
 #define DEBUG
+ */
 
 #ifdef HAVE_CONFIG_H
 #include <config.h>
diff --git a/libvips/iofuncs/sink.c b/libvips/iofuncs/sink.c
index 7ae86db3..84762b8e 100644
--- a/libvips/iofuncs/sink.c
+++ b/libvips/iofuncs/sink.c
@@ -338,7 +338,7 @@ vips_sink_tile( VipsImage *im,
 	Sink sink;
 	int result;
 
-	g_assert( !im_image_sanity( im ) );
+	g_assert( vips_object_sanity( VIPS_OBJECT( im ) ) );
 
 	/* We don't use this, but make sure it's set in case any old binaries
 	 * are expecting it.
diff --git a/libvips/iofuncs/sinkmemory.c b/libvips/iofuncs/sinkmemory.c
index ca8c89a2..56964e67 100644
--- a/libvips/iofuncs/sinkmemory.c
+++ b/libvips/iofuncs/sinkmemory.c
@@ -190,7 +190,7 @@ vips_sink_memory( VipsImage *im )
 	Sink sink;
 	int result;
 
-	g_assert( !im_image_sanity( im ) );
+	g_assert( vips_object_sanity( VIPS_OBJECT( im ) ) );
 
 	/* We don't use this, but make sure it's set in case any old binaries
 	 * are expecting it.