diff --git a/ChangeLog b/ChangeLog
index e5d90a26..70bf3200 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -12,6 +12,7 @@
 - lower priority for Matlab load to reduce segvs from Mat_Open(), thanks
   Michael
 - null-terminate libexif strings, thanks Mike
+- openslide always outputs solid pixels
 
 28/6/13 started 7.34.1
 - fix morphological operators on non-uchar images
diff --git a/libvips/foreign/openslide2vips.c b/libvips/foreign/openslide2vips.c
index 3d86cb2c..a2a7760b 100644
--- a/libvips/foreign/openslide2vips.c
+++ b/libvips/foreign/openslide2vips.c
@@ -37,6 +37,8 @@
  * 11/10/12
  * 	- look for tile-width and tile-height properties
  * 	- use threaded tile cache
+ * 6/8/13
+ * 	- always output solid (not transparent) pixels
  */
 
 /*
@@ -263,6 +265,7 @@ readslide_new( const char *filename, VipsImage *out,
 		return( NULL );
 	}
 
+
 	vips_image_init_fields( out, w, h, 4, VIPS_FORMAT_UCHAR,
 		VIPS_CODING_NONE, VIPS_INTERPRETATION_RGB, 1.0, 1.0 );
 
@@ -335,6 +338,15 @@ vips__openslide_generate( VipsRegion *out,
 
 	/* Convert from ARGB to RGBA and undo premultiplication. Since we are
 	 * inside a cache, we know buf must be continuous.
+	 *
+	 * We throw away transparency. Formats like Mirax use transparent + bg
+	 * colour for areas with no useful pixels. But if we output
+	 * transparent pixels and then convert to RGB for jpeg write later, we
+	 * would have to pass the bg colour down the pipe somehow. The
+	 * structure of dzsave makes this tricky.
+	 *
+	 * We could output plain RGB instead, but that would break
+	 * compatibility with older vipses.
 	 */
 	for( i = 0; i < n; i++ ) {
 		uint32_t *p = buf + i;
@@ -346,7 +358,7 @@ vips__openslide_generate( VipsRegion *out,
 			out[0] = 255 * ((x >> 16) & 255) / a;
 			out[1] = 255 * ((x >> 8) & 255) / a;
 			out[2] = 255 * (x & 255) / a;
-			out[3] = a;
+			out[3] = 255;
 		} 
 		else {
 			/* Use background color.
@@ -354,7 +366,7 @@ vips__openslide_generate( VipsRegion *out,
 			out[0] = (bg >> 16) & 255;
 			out[1] = (bg >> 8) & 255;
 			out[2] = bg & 255;
-			out[3] = 0;
+			out[3] = 255;
 		}
 	}
 
diff --git a/libvips/include/vips/internal.h b/libvips/include/vips/internal.h
index 6638d35f..7ecb9973 100644
--- a/libvips/include/vips/internal.h
+++ b/libvips/include/vips/internal.h
@@ -79,6 +79,10 @@ extern int vips__leak;
  */
 extern int vips__progress;
 
+/* Leak check on exit.
+ */
+extern int vips__leak;
+
 /* A string giving the image size (in bytes of uncompressed image) above which 
  * we decompress to disc on open. 
  */
diff --git a/libvips/include/vips/type.h b/libvips/include/vips/type.h
index 21da4807..1d6abb9b 100644
--- a/libvips/include/vips/type.h
+++ b/libvips/include/vips/type.h
@@ -91,6 +91,7 @@ typedef struct _VipsArea {
 
 VipsArea *vips_area_copy( VipsArea *area );
 void vips_area_unref( VipsArea *area );
+void vips__type_leak( void );
 
 VipsArea *vips_area_new( VipsCallbackFn free_fn, void *data );
 VipsArea *vips_area_new_blob( VipsCallbackFn free_fn, 
diff --git a/libvips/iofuncs/type.c b/libvips/iofuncs/type.c
index 84ecf351..c2303173 100644
--- a/libvips/iofuncs/type.c
+++ b/libvips/iofuncs/type.c
@@ -37,9 +37,9 @@
  */
 
 /*
+ */
 #define VIPS_DEBUG
 #define DEBUG
- */
 
 #ifdef HAVE_CONFIG_H
 #include <config.h>
@@ -150,7 +150,7 @@ vips_area_copy( VipsArea *area )
 {
 	g_mutex_lock( area->lock );
 
-	g_assert( area->count >= 0 );
+	g_assert( area->count > 0 );
 
 	area->count += 1;
 
@@ -176,8 +176,11 @@ vips_area_unref( VipsArea *area )
 	printf( "vips_area_unref: %p count = %d\n", area, area->count );
 #endif /*DEBUG*/
 
-	if( vips__leak )
+	if( vips__leak ) {
+		g_mutex_lock( vips__global_lock );
 		g_assert( g_slist_find( vips_area_all, area ) ); 
+		g_mutex_unlock( vips__global_lock );
+	}
 
 	if( area->count == 0 ) {
 		if( area->free_fn && area->data ) {
@@ -192,12 +195,17 @@ vips_area_unref( VipsArea *area )
 
 		g_free( area );
 
-		if( vips__leak )
+		if( vips__leak ) {
+			g_mutex_lock( vips__global_lock );
 			vips_area_all = g_slist_remove( vips_area_all, area ); 
+			g_mutex_unlock( vips__global_lock );
+		}
 
 #ifdef DEBUG
+		g_mutex_lock( vips__global_lock );
 		printf( "vips_area_unref: free .. total = %d\n", 
 			g_slist_length( vips_area_all ) );
+		g_mutex_unlock( vips__global_lock );
 #endif /*DEBUG*/
 	}
 	else
@@ -230,13 +238,18 @@ vips_area_new( VipsCallbackFn free_fn, void *data )
 	area->type = 0;
 	area->sizeof_type = 0;
 
-	if( vips__leak )
+	if( vips__leak ) {
+		g_mutex_lock( vips__global_lock );
 		vips_area_all = g_slist_prepend( vips_area_all, area ); 
+		g_mutex_unlock( vips__global_lock );
+	}
 
 #ifdef DEBUG
+	g_mutex_lock( vips__global_lock );
 	printf( "vips_area_new: %p count = %d (%d in total)\n", 
 		area, area->count, 
 		g_slist_length( vips_area_all ) );
+	g_mutex_unlock( vips__global_lock );
 #endif /*DEBUG*/
 
 	return( area );