diff -ru hplip-3.20.5.orig/scan/sane/escl.c hplip-3.20.5/scan/sane/escl.c
--- hplip-3.20.5.orig/scan/sane/escl.c	2020-05-11 16:34:00.000000000 +0300
+++ hplip-3.20.5/scan/sane/escl.c	2020-07-08 08:26:36.932679242 +0300
@@ -853,6 +853,14 @@
   /* Get scan parameters for sane client. */
   ps->bb_get_parameters(ps, params, ps->ip_handle ? SPO_STARTED : SPO_BEST_GUESS);
 
+  /* ADF has dynamic image height */
+  switch (ps->currentInputSource) {
+  case IS_ADF:
+  case IS_ADF_DUPLEX:
+    params->lines = -1;
+    break;
+  }
+
   /*_DBG("sane_hpaio_get_parameters(): format=%d, last_frame=%d, lines=%d, depth=%d, pixels_per_line=%d, bytes_per_line=%d\n",
     params->format, params->last_frame, params->lines, params->depth, params->pixels_per_line, params->bytes_per_line);
     */