diff --git a/doc/gpgsm.texi b/doc/gpgsm.texi
index 11c5c1962..e976767f6 100644
--- a/doc/gpgsm.texi
+++ b/doc/gpgsm.texi
@@ -554,6 +554,13 @@ Assume the input data is plain base-64 encoded.
 @opindex assume-binary
 Assume the input data is binary encoded.
 
+@item --input-size-hint @var{n}
+@opindex input-size-hint
+This option can be used to tell GPGSM the size of the input data in
+bytes.  @var{n} must be a positive base-10 number.  It is used by the
+@option{--status-fd} line ``PROGRESS'' to provide a value for
+``total'' if that is not available by other means.
+
 @anchor{option --p12-charset}
 @item --p12-charset @var{name}
 @opindex p12-charset
@@ -1721,6 +1728,9 @@ If @var{value} is true or @var{value} is not given all network access
 is disabled for this session.  This is the same as the command line
 option @option{--disable-dirmngr}.
 
+@item input-size-hint
+This is the same as the @option{--input-size-hint} command line option.
+
 @end table
 
 @mansect see also
diff --git a/sm/decrypt.c b/sm/decrypt.c
index abc1f2602..62983fe9c 100644
--- a/sm/decrypt.c
+++ b/sm/decrypt.c
@@ -1108,6 +1108,8 @@ gpgsm_decrypt (ctrl_t ctrl, int in_fd, estream_t out_fp)
     }
 
   gnupg_ksba_set_progress_cb (b64writer, gpgsm_progress_cb, ctrl);
+  if (ctrl->input_size_hint)
+    gnupg_ksba_set_total (b64writer, ctrl->input_size_hint);
 
   rc = ksba_cms_new (&cms);
   if (rc)
diff --git a/sm/encrypt.c b/sm/encrypt.c
index b0e59f73e..6e78a0620 100644
--- a/sm/encrypt.c
+++ b/sm/encrypt.c
@@ -654,6 +654,8 @@ gpgsm_encrypt (ctrl_t ctrl, certlist_t recplist, int data_fd, estream_t out_fp)
     }
 
   gnupg_ksba_set_progress_cb (b64writer, gpgsm_progress_cb, ctrl);
+  if (ctrl->input_size_hint)
+    gnupg_ksba_set_total (b64writer, ctrl->input_size_hint);
 
   err = ksba_cms_new (&cms);
   if (err)
diff --git a/sm/gpgsm.c b/sm/gpgsm.c
index 07c3ff480..ad7652c7d 100644
--- a/sm/gpgsm.c
+++ b/sm/gpgsm.c
@@ -139,6 +139,7 @@ enum cmd_and_opt_values {
   oAssumeArmor,
   oAssumeBase64,
   oAssumeBinary,
+  oInputSizeHint,
 
   oBase64,
   oNoArmor,
@@ -326,6 +327,7 @@ static gpgrt_opt_t opts[] = {
                 N_("assume input is in base-64 format")),
   ARGPARSE_s_n (oAssumeBinary, "assume-binary",
                 N_("assume input is in binary format")),
+  ARGPARSE_s_s (oInputSizeHint, "input-size-hint", "@"),
 
 
   ARGPARSE_header ("Output", N_("Options controlling the output")),
@@ -1188,6 +1190,10 @@ main ( int argc, char **argv)
           ctrl.is_base64 = 0;
           break;
 
+        case oInputSizeHint:
+          ctrl.input_size_hint = string_to_u64 (pargs.r.ret_str);
+          break;
+
         case oDisableCRLChecks:
           opt.no_crl_check = 1;
           break;
diff --git a/sm/gpgsm.h b/sm/gpgsm.h
index 46c77803d..e1aca8bb7 100644
--- a/sm/gpgsm.h
+++ b/sm/gpgsm.h
@@ -250,6 +250,11 @@ struct server_control_s
   int is_pem;         /* Is in PEM format */
   int is_base64;      /* is in plain base-64 format */
 
+  /* If > 0 a hint with the expected number of input data bytes.  This
+   * is not necessary an exact number but intended to be used for
+   * progress info and to decide on how to allocate buffers.  */
+  uint64_t input_size_hint;
+
   int create_base64;  /* Create base64 encoded output */
   int create_pem;     /* create PEM output */
   const char *pem_name; /* PEM name to use */
diff --git a/sm/server.c b/sm/server.c
index 1510590a7..b545c1bfb 100644
--- a/sm/server.c
+++ b/sm/server.c
@@ -298,6 +298,10 @@ option_handler (assuan_context_t ctx, const char *key, const char *value)
             opt.request_origin = i;
         }
     }
+  else if (!strcmp (key, "input-size-hint"))
+    {
+      ctrl->input_size_hint = string_to_u64 (value);
+    }
   else
     err = gpg_error (GPG_ERR_UNKNOWN_OPTION);
 
diff --git a/sm/sign.c b/sm/sign.c
index 4f5e8e3a0..235dac8cb 100644
--- a/sm/sign.c
+++ b/sm/sign.c
@@ -688,6 +688,8 @@ gpgsm_sign (ctrl_t ctrl, certlist_t signerlist,
     }
 
   gnupg_ksba_set_progress_cb (b64writer, gpgsm_progress_cb, ctrl);
+  if (ctrl->input_size_hint)
+    gnupg_ksba_set_total (b64writer, ctrl->input_size_hint);
 
   err = ksba_cms_new (&cms);
   if (err)
diff --git a/sm/verify.c b/sm/verify.c
index 9125b2b06..c7f4492ce 100644
--- a/sm/verify.c
+++ b/sm/verify.c
@@ -159,6 +159,8 @@ gpgsm_verify (ctrl_t ctrl, int in_fd, int data_fd, estream_t out_fp)
     }
 
   gnupg_ksba_set_progress_cb (b64writer, gpgsm_progress_cb, ctrl);
+  if (ctrl->input_size_hint)
+    gnupg_ksba_set_total (b64writer, ctrl->input_size_hint);
 
   rc = ksba_cms_new (&cms);
   if (rc)