diff --git a/newlib/libc/ctype/towctrans_l.c b/newlib/libc/ctype/towctrans_l.c
index 42085ac78..7b8a23c9c 100644
--- a/newlib/libc/ctype/towctrans_l.c
+++ b/newlib/libc/ctype/towctrans_l.c
@@ -39,7 +39,7 @@ static struct caseconv_entry {
   uint_least32_t first: 21;
   uint_least8_t diff: 8;
   uint_least8_t mode: 2;
-  uint_least32_t delta: 17;
+  int_least32_t delta: 17;
 } __attribute__ ((packed))
 caseconv_table [] = {
 #include "caseconv.t"