diff --git a/libvips/foreign/pforeign.h b/libvips/foreign/pforeign.h
index 83e5b8e0..d0773caa 100644
--- a/libvips/foreign/pforeign.h
+++ b/libvips/foreign/pforeign.h
@@ -187,7 +187,7 @@ int vips__png_write_target( VipsImage *in, VipsTarget *target,
 	int compress, int interlace, const char *profile,
 	VipsForeignPngFilter filter, gboolean strip,
 	gboolean palette, int Q, double dither,
-	int bitdepth );
+	int bitdepth, int effort );
 
 /* Map WEBP metadata names to vips names.
  */
@@ -217,7 +217,7 @@ int vips__webp_write_target( VipsImage *image, VipsTarget *target,
 
 int vips__quantise_image( VipsImage *in, 
 	VipsImage **index_out, VipsImage **palette_out,
-	int colours, int Q, double dither );
+	int colours, int Q, double dither, int effort );
 
 extern const char *vips_foreign_nifti_suffs[];
 
diff --git a/libvips/foreign/pngsave.c b/libvips/foreign/pngsave.c
index fcbdd112..ecdbb3a2 100644
--- a/libvips/foreign/pngsave.c
+++ b/libvips/foreign/pngsave.c
@@ -68,6 +68,7 @@ typedef struct _VipsForeignSavePng {
 	int Q;
 	double dither;
 	int bitdepth;
+	int effort;
 
 	/* Set by subclasses.
 	 */
@@ -153,7 +154,7 @@ vips_foreign_save_png_build( VipsObject *object )
 	if( vips__png_write_target( in, png->target,
 		png->compression, png->interlace, png->profile, png->filter,
 		save->strip, png->palette, png->Q, png->dither,
-		png->bitdepth ) ) {
+		png->bitdepth, png->effort ) ) {
 		g_object_unref( in );
 		return( -1 );
 	}
@@ -262,6 +263,13 @@ vips_foreign_save_png_class_init( VipsForeignSavePngClass *class )
 		G_STRUCT_OFFSET( VipsForeignSavePng, bitdepth ),
 		0, 8, 0 );
 
+	VIPS_ARG_INT( class, "effort", 18,
+		_( "Effort" ),
+		_( "Quantisation CPU effort" ),
+		VIPS_ARGUMENT_OPTIONAL_INPUT,
+		G_STRUCT_OFFSET( VipsForeignSavePng, effort ),
+		1, 10, 7 );
+
 	VIPS_ARG_INT( class, "colours", 14,
 		_( "Colours" ),
 		_( "Max number of palette colours" ),
@@ -278,6 +286,7 @@ vips_foreign_save_png_init( VipsForeignSavePng *png )
 	png->filter = VIPS_FOREIGN_PNG_FILTER_ALL;
 	png->Q = 100;
 	png->dither = 1.0;
+	png->effort = 7;
 }
 
 typedef struct _VipsForeignSavePngTarget {
@@ -464,6 +473,7 @@ vips_foreign_save_png_buffer_init( VipsForeignSavePngBuffer *buffer )
  * * @Q: %gint, quality for 8bpp quantisation 
  * * @dither: %gdouble, amount of dithering for 8bpp quantization
  * * @bitdepth: %int, set write bit depth to 1, 2, 4 or 8
+ * * @effort: %int, quantisation CPU effort
  *
  * Write a VIPS image to a file as PNG.
  *
@@ -492,8 +502,9 @@ vips_foreign_save_png_buffer_init( VipsForeignSavePngBuffer *buffer )
  *
  * Set @palette to %TRUE to enable palette mode for RGB or RGBA images. A
  * palette will be computed with enough space for @bitdepth (1, 2, 4 or 8) 
- * bits. Use @Q to set the optimisation effort, and @dither to set the degree of
- * Floyd-Steinberg dithering.
+ * bits. Use @Q to set the optimisation effort, @dither to set the degree of
+ * Floyd-Steinberg dithering and @effort to control the CPU effort
+ * (1 is the fastest, 10 is the slowest, 7 is the default).
  * This feature requires libvips to be compiled with libimagequant.
  *
  * You can also set @bitdepth for mono and mono + alpha images, and the image
@@ -536,6 +547,7 @@ vips_pngsave( VipsImage *in, const char *filename, ... )
  * * @Q: %gint, quality for 8bpp quantisation 
  * * @dither: %gdouble, amount of dithering for 8bpp quantization
  * * @bitdepth: %int, set write bit depth to 1, 2, 4 or 8
+ * * @effort: %int, quantisation CPU effort
  *
  * As vips_pngsave(), but save to a memory buffer. 
  *
@@ -591,6 +603,7 @@ vips_pngsave_buffer( VipsImage *in, void **buf, size_t *len, ... )
  * * @Q: quality for 8bpp quantisation 
  * * @dither: amount of dithering for 8bpp quantization
  * * @bitdepth: %int, set write bit depth to 1, 2, 4 or 8
+ * * @effort: %int, quantisation CPU effort
  *
  * As vips_pngsave(), but save to a target.
  *
diff --git a/libvips/foreign/quantise.c b/libvips/foreign/quantise.c
index 160d9b69..4bc10669 100644
--- a/libvips/foreign/quantise.c
+++ b/libvips/foreign/quantise.c
@@ -53,11 +53,12 @@
  */
 typedef struct _Quantise {
 	VipsImage *in;
-       	VipsImage **index_out;
-       	VipsImage **palette_out;
-        int colours;
-       	int Q;
-       	double dither;
+	VipsImage **index_out;
+	VipsImage **palette_out;
+	int colours;
+	int Q;
+	double dither;
+	int effort;
 
 	liq_attr *attr;
 	liq_image *input_image;
@@ -83,7 +84,7 @@ vips__quantise_free( Quantise *quantise )
 static Quantise *
 vips__quantise_new( VipsImage *in, 
 	VipsImage **index_out, VipsImage **palette_out,
-        int colours, int Q, double dither )
+        int colours, int Q, double dither, int effort )
 {
 	Quantise *quantise;
 	int i;
@@ -95,6 +96,7 @@ vips__quantise_new( VipsImage *in,
 	quantise->colours = colours;
 	quantise->Q = Q;
 	quantise->dither = dither;
+	quantise->effort = effort;
 	for( i = 0; i < VIPS_NUMBER( quantise->t ); i++ )
 		quantise->t[i] = NULL; 
 
@@ -104,7 +106,7 @@ vips__quantise_new( VipsImage *in,
 int
 vips__quantise_image( VipsImage *in, 
 	VipsImage **index_out, VipsImage **palette_out,
-	int colours, int Q, double dither )
+	int colours, int Q, double dither, int effort )
 {
 	Quantise *quantise;
 	VipsImage *index;
@@ -113,7 +115,7 @@ vips__quantise_image( VipsImage *in,
 	int i;
 
 	quantise = vips__quantise_new( in, index_out, palette_out, 
-		colours, Q, dither );
+		colours, Q, dither, effort );
 
 	/* Ensure input is sRGB. 
 	 */
@@ -145,13 +147,14 @@ vips__quantise_image( VipsImage *in,
 	quantise->attr = liq_attr_create();
 	liq_set_max_colors( quantise->attr, colours );
 	liq_set_quality( quantise->attr, 0, Q );
+	liq_set_speed( quantise->attr, 11 - effort );
 
 	quantise->input_image = liq_image_create_rgba( quantise->attr,
 		VIPS_IMAGE_ADDR( in, 0, 0 ), in->Xsize, in->Ysize, 0 );
 
 	if( liq_image_quantize( quantise->input_image, quantise->attr, 
 		&quantise->quantisation_result ) ) {
-		vips_error( "vips2png", "%s", _( "quantisation failed" ) );
+		vips_error( "quantise", "%s", _( "quantisation failed" ) );
 		vips__quantise_free( quantise ); 
 		return( -1 );
 	}
@@ -171,7 +174,7 @@ vips__quantise_image( VipsImage *in,
 	if( liq_write_remapped_image( quantise->quantisation_result, 
 		quantise->input_image,
 		VIPS_IMAGE_ADDR( index, 0, 0 ), VIPS_IMAGE_N_PELS( index ) ) ) {
-		vips_error( "vips2png", "%s", _( "quantisation failed" ) );
+		vips_error( "quantise", "%s", _( "quantisation failed" ) );
 		vips__quantise_free( quantise ); 
 		return( -1 );
 	}
diff --git a/libvips/foreign/vipspng.c b/libvips/foreign/vipspng.c
index 6b15b1c8..1915a819 100644
--- a/libvips/foreign/vipspng.c
+++ b/libvips/foreign/vipspng.c
@@ -986,7 +986,7 @@ write_vips( Write *write,
 	int compress, int interlace, const char *profile,
 	VipsForeignPngFilter filter, gboolean strip,
 	gboolean palette, int Q, double dither,
-	int bitdepth )
+	int bitdepth, int effort )
 {
 	VipsImage *in = write->in;
 
@@ -1162,7 +1162,7 @@ write_vips( Write *write,
 		int trans_count;
 
 		if( vips__quantise_image( in, &im_index, &im_palette, 
-			1 << bitdepth, Q, dither ) ) 
+			1 << bitdepth, Q, dither, effort ) )
 			return( -1 );
 
 		palette_count = im_palette->Xsize;
@@ -1256,7 +1256,7 @@ vips__png_write_target( VipsImage *in, VipsTarget *target,
 	int compression, int interlace,
 	const char *profile, VipsForeignPngFilter filter, gboolean strip,
 	gboolean palette, int Q, double dither,
-	int bitdepth )
+	int bitdepth, int effort )
 {
 	Write *write;
 
@@ -1265,7 +1265,7 @@ vips__png_write_target( VipsImage *in, VipsTarget *target,
 
 	if( write_vips( write, 
 		compression, interlace, profile, filter, strip, palette,
-		Q, dither, bitdepth ) ) {
+		Q, dither, bitdepth, effort ) ) {
 		write_destroy( write );
 		vips_error( "vips2png", _( "unable to write to target %s" ),
 			vips_connection_nick( VIPS_CONNECTION( target ) ) );