diff --git a/jtag/ChangeLog b/jtag/ChangeLog
index c0681339..2ea1ddbe 100644
--- a/jtag/ChangeLog
+++ b/jtag/ChangeLog
@@ -1,5 +1,10 @@
 2008-12-21  Kolja Waschk <kawk>
 
+   * src/tap/cable/ft2232.c, src/tap/cable/cmd_xfer.c,
+     src/tap/cable/cmd_xfer.h: limit maximum number of bytes queued 
+     into one cmd buffer. Should fix problems with high clocks count for
+     SVF runtest execution (Bug 2456024 - FTD2XX fails with certain SVF file)
+
    * configure.ac, src/tap/parport/direct.c: added detection of InpOut32
      library and support for using it for I/O port access even under Vista
 
diff --git a/jtag/src/tap/cable/cmd_xfer.c b/jtag/src/tap/cable/cmd_xfer.c
index 756284d5..91006d5d 100644
--- a/jtag/src/tap/cable/cmd_xfer.c
+++ b/jtag/src/tap/cable/cmd_xfer.c
@@ -61,6 +61,38 @@ extend_cmd_buffer( cx_cmd_t *cmd )
 }
 
 
+/*****************************************************************************
+ * cx_cmd_space( cmd, max_len )
+ *
+ * Return the difference between actually allocated bytes in the buffer of
+ * the current last command and max_len.  If there are already more bytes
+ * allocated than max_len, this function will return zero.
+ *
+ * cmd      : pointer to cx_cmd_t struct
+ * max_len  : upper limit for the space to allocate
+ *
+ * Return value:
+ * 0 : No space left
+ * >0: Number of bytes left
+ *
+ ****************************************************************************/
+int
+cx_cmd_space( cx_cmd_root_t *cmd_root, int max_len )
+{
+  int n;
+  cx_cmd_t *cmd = cmd_root->last;
+
+  if (!cmd)
+    return max_len;
+
+  n = max_len - cmd->buf_pos;
+  if (n < 0)
+    return 0;
+
+  return n;
+}
+
+
 /*****************************************************************************
  * cx_cmd_push( cmd, d )
  *
diff --git a/jtag/src/tap/cable/cmd_xfer.h b/jtag/src/tap/cable/cmd_xfer.h
index c10c2b2a..20b96ec6 100644
--- a/jtag/src/tap/cable/cmd_xfer.h
+++ b/jtag/src/tap/cable/cmd_xfer.h
@@ -47,6 +47,7 @@ struct cx_cmd_root {
 };
 typedef struct cx_cmd_root cx_cmd_root_t;
 
+int cx_cmd_space( cx_cmd_root_t *cmd_root, int max_len );
 int cx_cmd_push( cx_cmd_root_t *cmd_root, uint8_t d);
 cx_cmd_t *cx_cmd_dequeue( cx_cmd_root_t *cmd_root );
 void cx_cmd_free( cx_cmd_t *cmd );
diff --git a/jtag/src/tap/cable/ft2232.c b/jtag/src/tap/cable/ft2232.c
index cae8e4f9..e2630da6 100644
--- a/jtag/src/tap/cable/ft2232.c
+++ b/jtag/src/tap/cable/ft2232.c
@@ -931,6 +931,12 @@ ft2232_clock_schedule( cable_t *cable, int tms, int tdi, int n )
   cx_cmd_queue( cmd_root, 0 );
   while (n > 0)
   {
+    if (cx_cmd_space( cmd_root, 4096 ) < 3)
+    {
+      cx_xfer( cmd_root, &imm_cmd, cable, COMPLETELY );
+      cx_cmd_queue( cmd_root, 0 );
+    }
+
     /* Clock Data to TMS/CS Pin (no Read) */
     cx_cmd_push( cmd_root, MPSSE_WRITE_TMS |
                  MPSSE_LSB | MPSSE_BITMODE | MPSSE_WRITE_NEG );