diff --git a/lib/hcrypto/imath/imath.c b/lib/hcrypto/imath/imath.c
index 920e6ed26..ee7b69747 100755
--- a/lib/hcrypto/imath/imath.c
+++ b/lib/hcrypto/imath/imath.c
@@ -1769,7 +1769,7 @@ mp_result mp_int_read_cstring(mp_int z, mp_size radix, const char *str, char **e
     return MP_RANGE;
 
   /* Skip leading whitespace */
-  while(isspace((int)*str))
+  while(isspace((unsigned char)*str))
     ++str;
 
   /* Handle leading sign tag (+/-, positive default) */
@@ -3135,7 +3135,7 @@ static int       s_ch2val(char c, int r)
   if(isdigit((unsigned char) c))
     out = c - '0';
   else if(r > 10 && isalpha((unsigned char) c))
-    out = toupper(c) - 'A' + 10;
+      out = toupper((unsigned char)c) - 'A' + 10;
   else
     return -1;