diff --git a/libvips/conversion/sequential.c b/libvips/conversion/sequential.c
index 3483d1db..5f6def82 100644
--- a/libvips/conversion/sequential.c
+++ b/libvips/conversion/sequential.c
@@ -144,8 +144,8 @@ vips_sequential_generate( VipsRegion *or,
 		return( -1 );
 	}
 
-	if( r->top > sequential->y_pos &&
-		sequential->y_pos > 0 ) {
+	if( r->top > sequential->y_pos /* &&
+		sequential->y_pos > 0 */ ) {
 		/* We have started reading (y_pos > 0) and this request is for
 		 * stuff beyond that, stall for a while to give other
 		 * threads time to catch up.
diff --git a/libvips/foreign/jpeg2vips.c b/libvips/foreign/jpeg2vips.c
index 19c946fc..b2f7e562 100644
--- a/libvips/foreign/jpeg2vips.c
+++ b/libvips/foreign/jpeg2vips.c
@@ -893,8 +893,8 @@ read_jpeg_generate( VipsRegion *or,
 	int y;
 
 #ifdef DEBUG
-	printf( "read_jpeg_generate: line %d, %d rows\n", 
-		r->top, r->height );
+	printf( "read_jpeg_generate: %p line %d, %d rows\n", 
+		g_thread_self(), r->top, r->height );
 #endif /*DEBUG*/
 
 	VIPS_GATE_START( "read_jpeg_generate: work" );
diff --git a/libvips/iofuncs/sinkmemory.c b/libvips/iofuncs/sinkmemory.c
index 85ae4371..fca55963 100644
--- a/libvips/iofuncs/sinkmemory.c
+++ b/libvips/iofuncs/sinkmemory.c
@@ -180,7 +180,7 @@ sink_memory_area_allocate_fn( VipsThreadState *state, void *a, gboolean *stop )
 	VipsRect image;
 	VipsRect tile;
 
-	VIPS_DEBUG_MSG( "sink_memory_area_allocate_fn:\n" );
+	VIPS_DEBUG_MSG( "sink_memory_area_allocate_fn: %p\n", g_thread_self() );
 
 	/* Is the state x/y OK? New line or maybe new buffer or maybe even 
 	 * all done.
@@ -231,7 +231,8 @@ sink_memory_area_allocate_fn( VipsThreadState *state, void *a, gboolean *stop )
 	 */
 	wstate->area = memory->area;
 
-	VIPS_DEBUG_MSG( "  allocated %d x %d:\n", tile.left, tile.top );
+	VIPS_DEBUG_MSG( "  %p allocated %d x %d:\n", 
+		g_thread_self(), state->pos.left, state->pos.top );
 
 	/* Add to the number of writers on the area.
 	 */
@@ -260,13 +261,13 @@ sink_memory_area_work_fn( VipsThreadState *state, void *a )
 	int result;
 
 	VIPS_DEBUG_MSG( "sink_memory_area_work_fn: %p %d x %d\n", 
-		state, state->pos.left, state->pos.top );
+		g_thread_self(), state->pos.left, state->pos.top );
 
 	result = vips_region_prepare_to( state->reg, memory->region, 
 		&state->pos, state->pos.left, state->pos.top );
 
 	VIPS_DEBUG_MSG( "sink_memory_area_work_fn: %p result = %d\n", 
-		state, result );
+		g_thread_self(), result );
 
 	/* Tell the allocator we're done.
 	 */