diff --git a/gnu/usr.bin/tar/gnu.c b/gnu/usr.bin/tar/gnu.c
index ef51f2b5fedd..d3a04463082e 100644
--- a/gnu/usr.bin/tar/gnu.c
+++ b/gnu/usr.bin/tar/gnu.c
@@ -146,12 +146,12 @@ read_dir_file ()
 	strp[-1] = '\0';
       strp = buf;
       dev = atol (strp);
-      while (isdigit (*strp))
+      while (isdigit ((unsigned char) *strp))
 	strp++;
       ino = atol (strp);
-      while (isspace (*strp))
+      while (isspace ((unsigned char) *strp))
 	strp++;
-      while (isdigit (*strp))
+      while (isdigit ((unsigned char) *strp))
 	strp++;
       strp++;
       add_dir (un_quote_string (strp), dev, ino, (char *) 0);
diff --git a/gnu/usr.bin/tar/list.c b/gnu/usr.bin/tar/list.c
index 28e6ab316f1f..79d2654e3ade 100644
--- a/gnu/usr.bin/tar/list.c
+++ b/gnu/usr.bin/tar/list.c
@@ -513,7 +513,7 @@ from_oct (digs, where)
 {
   register long value;
 
-  while (isspace (*where))
+  while (isspace ((unsigned char) *where))
     {				/* Skip spaces */
       where++;
       if (--digs <= 0)
@@ -526,7 +526,7 @@ from_oct (digs, where)
       --digs;
     }
 
-  if (digs > 0 && *where && !isspace (*where))
+  if (digs > 0 && *where && !isspace ((unsigned char) *where))
     return -1;			/* Ended on non-space/nul */
 
   return value;