diff --git a/ChangeLog b/ChangeLog
index 089e03f9..cc39a182 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -34,6 +34,7 @@
   several of them before, causing a range of annoying problems
 - redone im_affine*() as a class
 - added input space displacement to affine
+- VipsArea is threadsafe
 
 14/11/12 started 7.30.6
 - capture tiff warnings earlier
diff --git a/doc/src/iosys.tex b/doc/src/iosys.tex
index 20e3195a..f79b797d 100644
--- a/doc/src/iosys.tex
+++ b/doc/src/iosys.tex
@@ -170,7 +170,7 @@ though \verb+im_open()+ is more useful.
 At the command-line, try:
 
 \begin{verbatim}
-$ vips --list classes
+$ vips list classes
 \end{verbatim}
 
 /noindent
diff --git a/doc/src/object.tex b/doc/src/object.tex
index 6f8bbad8..610c0953 100644
--- a/doc/src/object.tex
+++ b/doc/src/object.tex
@@ -129,6 +129,6 @@ A switch to the \verb+vips+ command-line program is handy for listing subtypes
 of \verb+VipsObject+. Try:
 
 \begin{verbatim}
-$ vips --list classes
+$ vips list classes
 \end{verbatim}
 
diff --git a/doc/src/packages.tex b/doc/src/packages.tex
index 8748078a..f3fde6b1 100644
--- a/doc/src/packages.tex
+++ b/doc/src/packages.tex
@@ -21,7 +21,7 @@ in the manual pages.
 
 \begin{fig2}
 \begin{verbatim}
-$ vips --list arithmetic
+$ vips list arithmetic
 im_abs               - absolute value
 im_acostra           - acos of image (result in degrees)
 im_add               - add two images
@@ -92,7 +92,7 @@ condition is true (or false) for a whole image.
 
 \begin{fig2}
 \begin{verbatim}
-$ vips --list relational
+$ vips list relational
 im_blend             - use cond image to blend between images in1 and in2
 im_equal             - two images equal in value
 im_equal_vec         - image equals doublevec
@@ -129,7 +129,7 @@ the relational and morphological functions. You can use
 
 \begin{fig2}
 \begin{verbatim}
-$ vips --list boolean
+$ vips list boolean
 im_andimage          - bitwise and of two images
 im_andimageconst     - bitwise and of an image with a constant
 im_andimage_vec      - bitwise and of an image with a vector constant
@@ -228,7 +228,7 @@ or \verb+disp+ colour space.
 
 \begin{fig2}
 \begin{verbatim}
-$ vips --list colour
+$ vips list colour
 im_LCh2Lab           - convert LCh to Lab
 im_LCh2UCS           - convert LCh to UCS
 im_Lab2LCh           - convert Lab to LCh
@@ -295,7 +295,7 @@ join of many images at the same time. See the manual pages.
 
 \begin{fig2}
 \begin{verbatim}
-$ vips --list conversion
+$ vips list conversion
 im_bandjoin          - bandwise join of two images
 im_bernd             - extract from pyramid as jpeg
 im_black             - generate black image
@@ -423,7 +423,7 @@ sections.
 
 \begin{fig2}
 \begin{verbatim}
-$ vips --list matrix
+$ vips list matrix
 im_matcat          - append matrix in2 to the end of matrix in1
 im_matinv          - invert matrix
 im_matmul          - multiply matrix in1 by matrix in2
@@ -469,7 +469,7 @@ expect.
 
 \begin{fig2}
 \begin{verbatim}
-$ vips --list convolution
+$ vips list convolution
 im_addgnoise         - add gaussian noise with mean 0 and std. dev. sigma
 im_compass           - convolve with 8-way rotating integer mask
 im_contrast_surface  - find high-contrast points in an image
@@ -535,7 +535,7 @@ not.
 
 \begin{fig2}
 \begin{verbatim}
-$ vips --list inplace
+$ vips list inplace
 im_circle          - plot circle on image
 im_flood_blob_copy - flood while pixel == start pixel
 im_insertplace     - draw image sub inside image main at position (x,y)
@@ -574,7 +574,7 @@ for an image.
 
 \begin{fig2}
 \begin{verbatim}
-$ vips --list freq_filt    
+$ vips list freq_filt    
 im_create_fmask    - create frequency domain filter mask
 im_disp_ps         - make displayable power spectrum
 im_flt_image_freq  - frequency domain filter image
@@ -614,7 +614,7 @@ functions are useful combinations of these basic operations.
 
 \begin{fig2}
 \begin{verbatim}
-$ vips --list histograms_lut
+$ vips list histograms_lut
 im_gammacorrect      - gamma-correct image
 im_heq               - histogram-equalise image
 im_hist              - find and graph histogram of image
@@ -695,7 +695,7 @@ union operations.
 
 \begin{fig2}
 \begin{verbatim}
-$ vips --list morphology
+$ vips list morphology
 im_cntlines        - count horizontal or vertical lines
 im_dilate          - dilate image with mask, adding a black border
 im_dilate_raw      - dilate image with mask
@@ -747,7 +747,7 @@ images.
 
 \begin{fig2}
 \begin{verbatim}
-$ vips --list mosaicing
+$ vips list mosaicing
 im_align_bands       - align the bands of an image
 im_correl            - search area around sec for match for area around ref
 im__find_lroverlap   - search for left-right overlap of ref and sec
@@ -780,7 +780,7 @@ They are useful for removing noise from images.
 
 \begin{fig2}
 \begin{verbatim}
-$ vips --list cimg
+$ vips list cimg
 im_greyc           - noise-removing filter
 im_greyc_mask      - noise-removing filter, with a mask
 \end{verbatim}
@@ -799,7 +799,7 @@ The \verb+im_benchmark*()+ operations are for testing the VIPS SMP system.
 
 \begin{fig2}
 \begin{verbatim}
-$ vips --list other
+$ vips list other
 im_benchmark       - do something complicated for testing
 im_benchmark2      - do something complicated for testing
 im_benchmarkn      - do something complicated for testing
@@ -823,7 +823,7 @@ These functions are related to the image IO system.
 
 \begin{fig2}
 \begin{verbatim}
-$ vips --list iofuncs
+$ vips list iofuncs
 im_binfile         - open a headerless binary file
 im_cache           - cache results of an operation
 im_guess_prefix    - guess install area
@@ -849,7 +849,7 @@ formats, see the man page for \verb+VipsFormat+.
 
 \begin{fig2}
 \begin{verbatim}
-$ vips --list format
+$ vips list format
 im_csv2vips          - read a file in csv format
 im_jpeg2vips         - convert from jpeg
 im_magick2vips       - load file with libMagick
@@ -877,7 +877,7 @@ These functions resample images with various interpolators.
 
 \begin{fig2}
 \begin{verbatim}
-$ vips --list resample
+$ vips list resample
 im_affine            - affine transform
 im_affinei           - affine transform
 im_affinei_all       - affine transform of whole image
diff --git a/libvips/foreign/dzsave.c b/libvips/foreign/dzsave.c
index e8bd1af3..fd6fa07a 100644
--- a/libvips/foreign/dzsave.c
+++ b/libvips/foreign/dzsave.c
@@ -1046,6 +1046,17 @@ vips_foreign_save_dz_build( VipsObject *object )
 			VIPS_SETSTR( dz->suffix, ".jpg" );
 	}
 
+	/* Default to white background. 
+	 */
+	if( dz->layout == VIPS_FOREIGN_DZ_LAYOUT_GOOGLE &&
+		!vips_object_argument_isset( object, "background" ) ) {
+		VipsArrayDouble *background; 
+
+		background = vips_array_double_newv( 1, 255.0 );
+		g_object_set( object, "background", background, NULL );
+		vips_area_unref( background ); 
+	}
+
 	if( dz->overlap >= dz->tile_size || 
 		dz->overlap >= dz->tile_size ) {
 		vips_error( "dzsave", 
@@ -1231,9 +1242,6 @@ vips_foreign_save_dz_init( VipsForeignSaveDz *dz )
 	dz->overlap = 1;
 	dz->tile_size = 256;
 	dz->tile_count = 0;
-	dz->background = 
-		vips_area_new_array( G_TYPE_DOUBLE, sizeof( double ), 1 ); 
-	((double *) (dz->background->data))[0] = 255;
 	dz->depth = VIPS_FOREIGN_DZ_DEPTH_1PIXEL; 
 }
 
diff --git a/libvips/include/vips/type.h b/libvips/include/vips/type.h
index 053ff11e..be96829d 100644
--- a/libvips/include/vips/type.h
+++ b/libvips/include/vips/type.h
@@ -66,9 +66,13 @@ typedef struct _VipsArea {
 
 	/*< private >*/
 
-	/* Reference count.
+	/* Reference count and lock. 
+	 *
+	 * We could use an atomic int, but this is not a high-traffic data
+	 * structure, so a simple GMutex is OK.
 	 */
 	int count;
+	GMutex *lock;		
 
 	/* Things like ICC profiles need their own free functions.
 	 */
diff --git a/libvips/iofuncs/type.c b/libvips/iofuncs/type.c
index dfe68915..cd80bfb1 100644
--- a/libvips/iofuncs/type.c
+++ b/libvips/iofuncs/type.c
@@ -147,6 +147,8 @@ static int vips_area_number = 0;
 VipsArea *
 vips_area_copy( VipsArea *area )
 {
+	g_mutex_lock( area->lock );
+
 	g_assert( area->count >= 0 );
 
 	area->count += 1;
@@ -155,12 +157,16 @@ vips_area_copy( VipsArea *area )
 	printf( "vips_area_copy: %p count = %d\n", area, area->count );
 #endif /*DEBUG*/
 
+	g_mutex_unlock( area->lock );
+
 	return( area );
 }
 
 void
 vips_area_unref( VipsArea *area )
 {
+	g_mutex_lock( area->lock );
+
 	g_assert( area->count > 0 );
 
 	area->count -= 1;
@@ -176,6 +182,10 @@ vips_area_unref( VipsArea *area )
 			area->free_fn = NULL;
 		}
 
+		g_mutex_unlock( area->lock );
+
+		VIPS_FREEF( vips_g_mutex_free, area->lock );
+
 		g_free( area );
 
 #ifdef DEBUG
@@ -184,6 +194,8 @@ vips_area_unref( VipsArea *area )
 			vips_area_number );
 #endif /*DEBUG*/
 	}
+	else
+		g_mutex_unlock( area->lock );
 }
 
 /**
@@ -205,6 +217,7 @@ vips_area_new( VipsCallbackFn free_fn, void *data )
 
 	area = g_new( VipsArea, 1 );
 	area->count = 1;
+	area->lock = vips_g_mutex_new();
 	area->length = 0;
 	area->data = data;
 	area->free_fn = free_fn;