Index: src/btree.c
==================================================================
--- src/btree.c
+++ src/btree.c
@@ -6647,10 +6647,11 @@
   */
   szScratch =
        nMaxCells*sizeof(u8*)                       /* apCell */
      + nMaxCells*sizeof(u16)                       /* szCell */
      + pBt->pageSize;                              /* aSpace1 */
+  assert( szScratch<=16896 || szScratch<=6*pBt->pageSize );
   apCell = sqlite3ScratchMalloc( szScratch ); 
   if( apCell==0 ){
     rc = SQLITE_NOMEM;
     goto balance_cleanup;
   }

Index: src/sqlite.h.in
==================================================================
--- src/sqlite.h.in
+++ src/sqlite.h.in
@@ -1537,14 +1537,18 @@
 ** drawn, the size of each scratch allocation (sz),
 ** and the maximum number of scratch allocations (N).  The sz
 ** argument must be a multiple of 16.
 ** The first argument must be a pointer to an 8-byte aligned buffer
 ** of at least sz*N bytes of memory.
-** ^SQLite will use no more than two scratch buffers per thread.  So
-** N should be set to twice the expected maximum number of threads.
-** ^SQLite will never require a scratch buffer that is more than 6
-** times the database page size. ^If SQLite needs needs additional
+** ^SQLite will not use more than two scratch buffers per thread and not
+** more than one scratch buffer per thread when not performing
+** a [checkpoint] in [WAL mode].
+** ^SQLite will never request a scratch buffer that is more than 6
+** times the database page size, except when performing a [checkpoint]
+** in [WAL mode] when the scratch buffer request size is a small fraction
+** of the size of the WAL file.
+** ^If SQLite needs needs additional
 ** scratch memory beyond what is provided by this configuration option, then 
 ** [sqlite3_malloc()] will be used to obtain the memory needed.</dd>
 **
 ** [[SQLITE_CONFIG_PAGECACHE]] <dt>SQLITE_CONFIG_PAGECACHE</dt>
 ** <dd> ^This option specifies a static memory buffer that SQLite can use for