Index: ext/fts3/fts3.c
==================================================================
--- ext/fts3/fts3.c
+++ ext/fts3/fts3.c
@@ -2578,10 +2578,12 @@
     }else{
       fts3PutDeltaVarint3(&p, bDescDoclist, &iPrev, &bFirstOut, i2);
       fts3PoslistCopy(&p, &p2);
       fts3GetDeltaVarint3(&p2, pEnd2, bDescDoclist, &i2);
     }
+    
+    assert( (p-aOut)<=((p1?(p1-a1):n1)+(p2?(p2-a2):n2)+FTS3_VARINT_MAX-1) );
   }
 
   if( rc!=SQLITE_OK ){
     sqlite3_free(aOut);
     p = aOut = 0;

Index: src/test_hexio.c
==================================================================
--- src/test_hexio.c
+++ src/test_hexio.c
@@ -335,10 +335,21 @@
   x += y * (*q++);
   *v = (sqlite_int64) x;
   return (int) (q - (unsigned char *)p);
 }
 
+static int putFts3Varint(char *p, sqlite_int64 v){
+  unsigned char *q = (unsigned char *) p;
+  sqlite_uint64 vu = v;
+  do{
+    *q++ = (unsigned char) ((vu & 0x7f) | 0x80);
+    vu >>= 7;
+  }while( vu!=0 );
+  q[-1] &= 0x7f;  /* turn off high bit in final byte */
+  assert( q - (unsigned char *)p <= 10 );
+  return (int) (q - (unsigned char *)p);
+}
 
 /*
 ** USAGE:  read_fts3varint BLOB VARNAME
 **
 ** Read a varint from the start of BLOB. Set variable VARNAME to contain
@@ -365,10 +376,72 @@
   Tcl_ObjSetVar2(interp, objv[2], 0, Tcl_NewWideIntObj(iVal), 0);
   Tcl_SetObjResult(interp, Tcl_NewIntObj(nVal));
   return TCL_OK;
 }
 
+/*
+** USAGE:  make_fts3record ARGLIST
+*/
+static int SQLITE_TCLAPI make_fts3record(
+  void * clientData,
+  Tcl_Interp *interp,
+  int objc,
+  Tcl_Obj *CONST objv[]
+){
+  Tcl_Obj **aArg = 0;
+  int nArg = 0;
+  unsigned char *aOut = 0;
+  int nOut = 0;
+  int nAlloc = 0;
+  int i;
+  int rc = TCL_OK;
+
+  if( objc!=2 ){
+    Tcl_WrongNumArgs(interp, 1, objv, "LIST");
+    return TCL_ERROR;
+  }
+  if( Tcl_ListObjGetElements(interp, objv[1], &nArg, &aArg) ){
+    return TCL_ERROR;
+  }
+
+  for(i=0; i<nArg; i++){
+    sqlite3_int64 iVal;
+    if( TCL_OK==Tcl_GetWideIntFromObj(0, aArg[i], &iVal) ){
+      if( nOut+10>nAlloc ){
+        int nNew = nAlloc?nAlloc*2:128;
+        unsigned char *aNew = sqlite3_realloc(aOut, nNew);
+        if( aNew==0 ){
+          sqlite3_free(aOut);
+          return TCL_ERROR;
+        }
+        aOut = aNew;
+        nAlloc = nNew;
+      }
+      nOut += putFts3Varint((char*)&aOut[nOut], iVal);
+    }else{
+      int nVal = 0;
+      char *zVal = Tcl_GetStringFromObj(aArg[i], &nVal);
+      while( (nOut + nVal)>nAlloc ){
+        int nNew = nAlloc?nAlloc*2:128;
+        unsigned char *aNew = sqlite3_realloc(aOut, nNew);
+        if( aNew==0 ){
+          sqlite3_free(aOut);
+          return TCL_ERROR;
+        }
+        aOut = aNew;
+        nAlloc = nNew;
+      }
+      memcpy(&aOut[nOut], zVal, nVal);
+      nOut += nVal;
+    }
+  }
+
+  Tcl_SetObjResult(interp, Tcl_NewByteArrayObj(aOut, nOut));
+  sqlite3_free(aOut);
+  return TCL_OK;
+}
+
 
 /*
 ** Register commands with the TCL interpreter.
 */
 int Sqlitetest_hexio_Init(Tcl_Interp *interp){
@@ -381,12 +454,13 @@
      { "hexio_get_int",                hexio_get_int         },
      { "hexio_render_int16",           hexio_render_int16    },
      { "hexio_render_int32",           hexio_render_int32    },
      { "utf8_to_utf8",                 utf8_to_utf8          },
      { "read_fts3varint",              read_fts3varint       },
+     { "make_fts3record",              make_fts3record       },
   };
   int i;
   for(i=0; i<sizeof(aObjCmd)/sizeof(aObjCmd[0]); i++){
     Tcl_CreateObjCommand(interp, aObjCmd[i].zName, aObjCmd[i].xProc, 0, 0);
   }
   return TCL_OK;
 }

ADDED   test/fts4record.test
Index: test/fts4record.test
==================================================================
--- /dev/null
+++ test/fts4record.test
@@ -0,0 +1,120 @@
+# 2019 September 18
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#*************************************************************************
+# This file implements regression tests for SQLite library.  The
+# focus of this script is testing the FTS4 module.
+#
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+source $testdir/fts3_common.tcl
+set testprefix fts4record
+
+# If SQLITE_ENABLE_FTS3 is defined, omit this file.
+ifcapable !fts3 {
+  finish_test
+  return
+}
+
+sqlite3_fts3_may_be_corrupt 1
+
+do_execsql_test 1.0 {
+  CREATE VIRTUAL TABLE t1 USING fts4(x);
+  INSERT INTO t1 VALUES('terma terma terma termb');
+}
+
+do_execsql_test 1.1 {
+  SELECT quote(root) FROM t1_segdir
+} {
+  X'00057465726D6105010203030004016203010500'
+}
+
+proc make_record_wrapper {args} { make_fts3record $args }
+db func record make_record_wrapper
+
+do_execsql_test 1.2 {
+  select quote( 
+    record(0,    5, 'terma', 5, 1, 2, 3, 3, 0, 
+              4, 1, 'b'    , 3, 1, 5, 0
+  ) );
+} {
+  X'00057465726D6105010203030004016203010500'
+}
+
+do_execsql_test 1.3.1 {
+  UPDATE t1_segdir SET root = 
+    record(0,    5, 'terma', 5, 1, 2, 3, 3, 0, 
+              4, 1, 'b'    , 3, 1, 5, 
+              1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+              1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+              1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0
+          );
+}
+
+do_catchsql_test 1.3.2 {
+  SELECT snippet(t1) FROM t1 WHERE t1 MATCH 'term*'
+} {1 {database disk image is malformed}}
+
+do_execsql_test 1.4.1 {
+  UPDATE t1_segdir SET root = 
+    record(0,    5, 'terma', 5, 1, 2, 3, 3, 0, 
+              4, 1, 'b'    , 4, 1, 5, 
+              256, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+              1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+              1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0
+          );
+}
+
+do_catchsql_test 1.4.2 {
+  SELECT snippet(t1) FROM t1 WHERE t1 MATCH 'term*'
+} {1 {database disk image is malformed}}
+
+do_execsql_test 1.4.3 {
+  SELECT quote(root) FROM t1_segdir
+} {
+  X'00057465726D610501020303000401620401058002010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010100'
+}
+
+do_execsql_test 1.5.1 {
+  UPDATE t1_segdir SET root = 
+    record(0,    5, 'terma', 5, 1, 2, 3, 3, 0, 
+              4, 1, 'b'    , 4, 1, 5, 
+              256, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+              1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+              1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0
+          );
+}
+
+do_catchsql_test 1.4.2 {
+  SELECT snippet(t1) FROM t1 WHERE t1 MATCH 'term*'
+} {1 {database disk image is malformed}}
+
+do_execsql_test 1.4.3 {
+  SELECT quote(root) FROM t1_segdir
+} {
+  X'00057465726D610501020303000401620401058002010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010100'
+}
+
+
+do_execsql_test 1.5.1 {
+  UPDATE t1_segdir SET root = 
+  X'00057465726D61050102030300040162040105FF00010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010100'
+}
+
+do_catchsql_test 1.5.2 {
+  SELECT snippet(t1) FROM t1 WHERE t1 MATCH 'term*'
+} {1 {database disk image is malformed}}
+
+do_catchsql_test 1.5.3 {
+  INSERT INTO t1(t1) VALUES('integrity-check');
+} {1 {database disk image is malformed}}
+
+finish_test