Index: src/alter.c
==================================================================
--- src/alter.c
+++ src/alter.c
@@ -72,11 +72,11 @@
       */
       do {
         zCsr += len;
         len = sqlite3GetToken(zCsr, &token);
       } while( token==TK_SPACE );
-      assert( len>0 );
+      assert( len>0 || !*zCsr );
     } while( token!=TK_LP && token!=TK_USING );
 
     zRet = sqlite3MPrintf(db, "%.*s\"%w\"%s", (int)(((u8*)tname.z) - zSql),
        zSql, zTableName, tname.z+tname.n);
     sqlite3_result_text(context, zRet, -1, SQLITE_DYNAMIC);
@@ -196,11 +196,11 @@
       */
       do {
         zCsr += len;
         len = sqlite3GetToken(zCsr, &token);
       }while( token==TK_SPACE );
-      assert( len>0 );
+      assert( len>0 || !*zCsr );
 
       /* Variable 'dist' stores the number of tokens read since the most
       ** recent TK_DOT or TK_ON. This means that when a WHEN, FOR or BEGIN 
       ** token is read and 'dist' equals 2, the condition stated above
       ** to be met.

Index: src/tokenize.c
==================================================================
--- src/tokenize.c
+++ src/tokenize.c
@@ -52,15 +52,16 @@
 #define CC_COMMA     23    /* ',' */
 #define CC_AND       24    /* '&' */
 #define CC_TILDA     25    /* '~' */
 #define CC_DOT       26    /* '.' */
 #define CC_ILLEGAL   27    /* Illegal character */
+#define CC_NUL       28    /* 0x00 */
 
 static const unsigned char aiClass[] = {
 #ifdef SQLITE_ASCII
 /*         x0  x1  x2  x3  x4  x5  x6  x7  x8  x9  xa  xb  xc  xd  xe  xf */
-/* 0x */   27, 27, 27, 27, 27, 27, 27, 27, 27,  7,  7, 27,  7,  7, 27, 27,
+/* 0x */   28, 27, 27, 27, 27, 27, 27, 27, 27,  7,  7, 27,  7,  7, 27, 27,
 /* 1x */   27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
 /* 2x */    7, 15,  8,  5,  4, 22, 24,  8, 17, 18, 21, 20, 23, 11, 26, 16,
 /* 3x */    3,  3,  3,  3,  3,  3,  3,  3,  3,  3,  5, 19, 12, 14, 13,  6,
 /* 4x */    5,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
 /* 5x */    1,  1,  1,  1,  1,  1,  1,  1,  0,  1,  1,  9, 27, 27, 27,  1,
@@ -529,10 +530,14 @@
       ** SQL keywords start with the letter 'x'.  Fall through */
     }
     case CC_ID: {
       i = 1;
       break;
+    }
+    case CC_NUL: {
+      *tokenType = TK_ILLEGAL;
+      return 0;
     }
     default: {
       *tokenType = TK_ILLEGAL;
       return 1;
     }