https://sqlite.org/src/info/42f0777555675875

--- ext/misc/csv.c
+++ ext/misc/csv.c
@@ -78,7 +78,7 @@
   int nAlloc;            /* Space allocated for z[] */
   int nLine;             /* Current line number */
   int bNotFirst;         /* True if prior text has been seen */
-  char cTerm;            /* Character that terminated the most recent field */
+  int cTerm;             /* Character that terminated the most recent field */
   size_t iIn;            /* Next unread character in the input buffer */
   size_t nIn;            /* Number of characters in the input buffer */
   char *zIn;             /* The input buffer */
@@ -166,7 +166,7 @@
     if( p->in!=0 ) return csv_getc_refill(p);
     return EOF;
   }
-  return p->zIn[p->iIn++];
+  return ((unsigned char*)p->zIn)[p->iIn++];
 }
 
 /* Increase the size of p->z and append character c to the end. 
--- test/releasetest.tcl
+++ test/releasetest.tcl
@@ -114,7 +114,7 @@
   }
   "Debug-One" {
     --disable-shared
-    -O2
+    -O2 -funsigned-char
     -DSQLITE_DEBUG=1
     -DSQLITE_MEMDEBUG=1
     -DSQLITE_MUTEX_NOOP=1