diff --git a/bgpd/bgp_mplsvpn.c b/bgpd/bgp_mplsvpn.c
index 72ad089..c1f1fbb 100644
--- a/bgpd/bgp_mplsvpn.c
+++ b/bgpd/bgp_mplsvpn.c
@@ -233,9 +233,13 @@
   char *endptr;
   u_int32_t t;
 
-  l = strtoul (str, &endptr, 10);
+  if (*str == '-')
+    return 0;
   
-  if (*endptr == '\0' || l == ULONG_MAX || l > UINT32_MAX)
+  errno = 0;
+  l = strtoul (str, &endptr, 10);
+
+  if (*endptr != '\0' || errno || l > UINT32_MAX)
     return 0;
 
   t = (u_int32_t) l;
diff --git a/bgpd/bgp_routemap.c b/bgpd/bgp_routemap.c
index 173bf93..42c3e05 100644
--- a/bgpd/bgp_routemap.c
+++ b/bgpd/bgp_routemap.c
@@ -525,8 +525,13 @@
   char *endptr = NULL;
   unsigned long tmpval;
 
+  /* Metric value shoud be integer. */
+  if (! all_digit (arg))
+    return NULL;
+
+  errno = 0;
   tmpval = strtoul (arg, &endptr, 10);
-  if (*endptr != '\0' || tmpval == ULONG_MAX || tmpval > UINT32_MAX)
+  if (*endptr != '\0' || errno || tmpval > UINT32_MAX)
     return NULL;
     
   med = XMALLOC (MTYPE_ROUTE_MAP_COMPILED, sizeof (u_int32_t));
@@ -1002,8 +1007,9 @@
   if (! all_digit (arg))
     return NULL;
   
+  errno = 0;
   tmp = strtoul (arg, &endptr, 10);
-  if (*endptr != '\0' || tmp == ULONG_MAX || tmp > UINT32_MAX)
+  if (*endptr != '\0' || errno || tmp > UINT32_MAX)
     return NULL;
    
   local_pref = XMALLOC (MTYPE_ROUTE_MAP_COMPILED, sizeof (u_int32_t)); 
@@ -1070,9 +1076,9 @@
   if (! all_digit (arg))
     return NULL;
 
-
+  errno = 0;
   tmp = strtoul (arg, &endptr, 10);
-  if (*endptr != '\0' || tmp == ULONG_MAX || tmp > UINT32_MAX)
+  if (*endptr != '\0' || errno || tmp > UINT32_MAX)
     return NULL;
   
   weight = XMALLOC (MTYPE_ROUTE_MAP_COMPILED, sizeof (u_int32_t));
@@ -1161,8 +1167,9 @@
   if (all_digit (arg))
     {
       /* set metric value check*/
+      errno = 0;
       larg = strtoul (arg, &endptr, 10);
-      if (*endptr != '\0' || larg == ULONG_MAX || larg > UINT32_MAX)
+      if (*endptr != '\0' || errno || larg > UINT32_MAX)
         return NULL;
       metric = larg;
     }
@@ -1174,8 +1181,9 @@
 	   || (! all_digit (arg+1)))
 	return NULL;
 
+      errno = 0;
       larg = strtoul (arg+1, &endptr, 10);
-      if (*endptr != '\0' || larg == ULONG_MAX || larg > UINT32_MAX)
+      if (*endptr != '\0' || errno || larg > UINT32_MAX)
 	return NULL;
       metric = larg;
     }
diff --git a/lib/vty.h b/lib/vty.h
index 7df04b5..639d741 100644
--- a/lib/vty.h
+++ b/lib/vty.h
@@ -152,8 +152,9 @@
 #define VTY_GET_LONG(NAME,V,STR) \
 do { \
   char *endptr = NULL; \
+  errno = 0; \
   (V) = strtoul ((STR), &endptr, 10); \
-  if (*endptr != '\0' || (V) == ULONG_MAX) \
+  if (*(STR) == '-' || *endptr != '\0' || errno) \
     { \
       vty_out (vty, "%% Invalid %s value%s", NAME, VTY_NEWLINE); \
       return CMD_WARNING; \
diff --git a/ospfd/ospf_vty.c b/ospfd/ospf_vty.c
index 577e417..f68adb2 100644
--- a/ospfd/ospf_vty.c
+++ b/ospfd/ospf_vty.c
@@ -80,8 +80,11 @@
   /* match "<0-4294967295>". */
   else
     {
+      if (*str == '-')
+        return -1;
+      errno = 0;
       ret = strtoul (str, &endptr, 10);
-      if (*endptr != '\0' || (ret == ULONG_MAX && errno == ERANGE))
+      if (*endptr != '\0' || errno || ret > UINT32_MAX)
         return -1;
 
       area_id->s_addr = htonl (ret);