diff --git a/libvips/foreign/jpegload.c b/libvips/foreign/jpegload.c
index 9e53914e..bc0e2559 100644
--- a/libvips/foreign/jpegload.c
+++ b/libvips/foreign/jpegload.c
@@ -169,14 +169,6 @@ typedef VipsForeignLoadJpegClass VipsForeignLoadJpegFileClass;
 G_DEFINE_TYPE( VipsForeignLoadJpegFile, vips_foreign_load_jpeg_file, 
 	vips_foreign_load_jpeg_get_type() );
 
-static VipsForeignFlags
-vips_foreign_load_jpeg_file_get_flags_filename( const char *filename )
-{
-	/* The jpeg reader supports sequential read.
-	 */
-	return( VIPS_FOREIGN_SEQUENTIAL );
-}
-
 static gboolean
 vips_foreign_load_jpeg_file_is_a( const char *filename )
 {
@@ -232,8 +224,6 @@ vips_foreign_load_jpeg_file_class_init( VipsForeignLoadJpegFileClass *class )
 	 */
 	foreign_class->priority = 50;
 
-	load_class->get_flags_filename = 
-		vips_foreign_load_jpeg_file_get_flags_filename;
 	load_class->is_a = vips_foreign_load_jpeg_file_is_a;
 	load_class->header = vips_foreign_load_jpeg_file_header;
 	load_class->load = vips_foreign_load_jpeg_file_load;
diff --git a/libvips/foreign/pforeign.h b/libvips/foreign/pforeign.h
index 26804bee..796c1d38 100644
--- a/libvips/foreign/pforeign.h
+++ b/libvips/foreign/pforeign.h
@@ -183,6 +183,7 @@ int vips__png_read( const char *name, VipsImage *out, gboolean readbehind );
 gboolean vips__png_ispng_buffer( const void *buf, size_t len );
 int vips__png_ispng( const char *filename );
 gboolean vips__png_isinterlaced( const char *filename );
+gboolean vips__png_isinterlaced_buffer( const void *buffer, size_t length );
 extern const char *vips__png_suffs[];
 int vips__png_read_buffer( const void *buffer, size_t length, 
 	VipsImage *out, gboolean readbehind  );
diff --git a/libvips/foreign/pngload.c b/libvips/foreign/pngload.c
index 7f2f8fc0..f2bb9328 100644
--- a/libvips/foreign/pngload.c
+++ b/libvips/foreign/pngload.c
@@ -167,12 +167,29 @@ typedef VipsForeignLoadClass VipsForeignLoadPngBufferClass;
 G_DEFINE_TYPE( VipsForeignLoadPngBuffer, vips_foreign_load_png_buffer, 
 	VIPS_TYPE_FOREIGN_LOAD );
 
+static VipsForeignFlags
+vips_foreign_load_png_buffer_get_flags( VipsForeignLoad *load )
+{
+	VipsForeignLoadPngBuffer *buffer = (VipsForeignLoadPngBuffer *) load;
+
+	VipsForeignFlags flags;
+
+	flags = 0;
+	if( vips__png_isinterlaced_buffer( buffer->buf->data, 
+		buffer->buf->length ) )
+		flags |= VIPS_FOREIGN_PARTIAL;
+	else
+		flags |= VIPS_FOREIGN_SEQUENTIAL;
+
+	return( flags );
+}
+
 static int
 vips_foreign_load_png_buffer_header( VipsForeignLoad *load )
 {
-	VipsForeignLoadPngBuffer *png = (VipsForeignLoadPngBuffer *) load;
+	VipsForeignLoadPngBuffer *buffer = (VipsForeignLoadPngBuffer *) load;
 
-	if( vips__png_header_buffer( png->buf->data, png->buf->length, 
+	if( vips__png_header_buffer( buffer->buf->data, buffer->buf->length, 
 		load->out ) )
 		return( -1 );
 
@@ -182,9 +199,9 @@ vips_foreign_load_png_buffer_header( VipsForeignLoad *load )
 static int
 vips_foreign_load_png_buffer_load( VipsForeignLoad *load )
 {
-	VipsForeignLoadPngBuffer *png = (VipsForeignLoadPngBuffer *) load;
+	VipsForeignLoadPngBuffer *buffer = (VipsForeignLoadPngBuffer *) load;
 
-	if( vips__png_read_buffer( png->buf->data, png->buf->length, 
+	if( vips__png_read_buffer( buffer->buf->data, buffer->buf->length, 
 		load->real, load->access == VIPS_ACCESS_SEQUENTIAL ) )
 		return( -1 );
 
@@ -218,7 +235,7 @@ vips_foreign_load_png_buffer_class_init( VipsForeignLoadPngBufferClass *class )
 }
 
 static void
-vips_foreign_load_png_buffer_init( VipsForeignLoadPngBuffer *png )
+vips_foreign_load_png_buffer_init( VipsForeignLoadPngBuffer *buffer )
 {
 }
 
diff --git a/libvips/foreign/vipspng.c b/libvips/foreign/vipspng.c
index cbd6b23f..46324377 100644
--- a/libvips/foreign/vipspng.c
+++ b/libvips/foreign/vipspng.c
@@ -710,6 +710,28 @@ vips__png_read_buffer( const void *buffer, size_t length, VipsImage *out,
 	return( 0 );
 }
 
+/* Interlaced PNGs need to be entirely decompressed into memory then can be
+ * served partially from there. Non-interlaced PNGs may be read sequentially.
+ */
+gboolean
+vips__png_isinterlaced_buffer( const void *buffer, size_t length )
+{
+	VipsImage *image;
+	Read *read;
+	int interlace_type;
+
+	image = vips_image_new();
+
+	if( !(read = read_new_buffer( image, buffer, length, FALSE )) ) { 
+		g_object_unref( image );
+		return( -1 );
+	}
+	interlace_type = png_get_interlace_type( read->pPng, read->pInfo );
+	g_object_unref( image );
+
+	return( interlace_type != PNG_INTERLACE_NONE );
+}
+
 const char *vips__png_suffs[] = { ".png", NULL };
 
 /* What we track during a PNG write.