Index: src/os_unix.c
==================================================================
--- src/os_unix.c
+++ src/os_unix.c
@@ -3856,10 +3856,18 @@
       i64 newLimit = *(i64*)pArg;
       int rc = SQLITE_OK;
       if( newLimit>sqlite3GlobalConfig.mxMmap ){
         newLimit = sqlite3GlobalConfig.mxMmap;
       }
+
+      /* The value of newLimit may be eventually cast to (size_t) and passed
+      ** to mmap(). Restrict its value to 2GB if (size_t) is not at least a
+      ** 64-bit type. */
+      if( newLimit>0 && sizeof(size_t)<8 ){
+        newLimit = (newLimit & 0x7FFFFFFF);
+      }
+
       *(i64*)pArg = pFile->mmapSizeMax;
       if( newLimit>=0 && newLimit!=pFile->mmapSizeMax && pFile->nFetchOut==0 ){
         pFile->mmapSizeMax = newLimit;
         if( pFile->mmapSize>0 ){
           unixUnmapfile(pFile);

Index: src/os_win.c
==================================================================
--- src/os_win.c
+++ src/os_win.c
@@ -3557,10 +3557,18 @@
       i64 newLimit = *(i64*)pArg;
       int rc = SQLITE_OK;
       if( newLimit>sqlite3GlobalConfig.mxMmap ){
         newLimit = sqlite3GlobalConfig.mxMmap;
       }
+
+      /* The value of newLimit may be eventually cast to (SIZE_T) and passed
+      ** to MapViewOfFile(). Restrict its value to 2GB if (SIZE_T) is not at
+      ** least a 64-bit type. */
+      if( newLimit>0 && sizeof(SIZE_T)<8 ){
+        newLimit = (newLimit & 0x7FFFFFFF);
+      }
+
       *(i64*)pArg = pFile->mmapSizeMax;
       if( newLimit>=0 && newLimit!=pFile->mmapSizeMax && pFile->nFetchOut==0 ){
         pFile->mmapSizeMax = newLimit;
         if( pFile->mmapSize>0 ){
           winUnmapfile(pFile);

Index: test/bigmmap.test
==================================================================
--- test/bigmmap.test
+++ test/bigmmap.test
@@ -28,11 +28,11 @@
 set mmap_limit 0
 db eval { 
   SELECT compile_options AS x FROM pragma_compile_options 
   WHERE x LIKE 'max_mmap_size=%' 
 } {
-  regexp {MAX_MMAP_SIZE=(.*)} $x -> mmap_limit
+  regexp {MAX_MMAP_SIZE=([0-9]*)} $x -> mmap_limit
 }
 if {$mmap_limit < [expr 8 * 1<<30]} {
   puts "Skipping bigmmap.test - requires SQLITE_MAX_MMAP_SIZE >= 8G"
   finish_test
   return