diff --git a/commandline.c b/commandline.c
index bafce311..7ab41741 100644
--- a/commandline.c
+++ b/commandline.c
@@ -761,7 +761,7 @@ int app_server_status(int argc, const char *const *argv, struct command_line_opt
 int app_mdp_ping(int argc, const char *const *argv, struct command_line_option *o)
 {
   const char *sid;
-  if (cli_arg(argc, argv, o, "SID|broadcast", &sid, validateSid, "broadcast") == -1)
+  if (cli_arg(argc, argv, o, "SID|broadcast", &sid, str_is_subscriber_id, "broadcast") == -1)
     return -1;
 
   overlay_mdp_frame mdp;
@@ -961,7 +961,7 @@ int app_rhizome_hash_file(int argc, const char *const *argv, struct command_line
 
 int cli_optional_sid(const char *arg)
 {
-  return !arg[0] || validateSid(arg);
+  return !arg[0] || str_is_subscriber_id(arg);
 }
 
 int cli_optional_bundle_key(const char *arg)
diff --git a/dataformats.c b/dataformats.c
index 3d4130bc..527bebfe 100644
--- a/dataformats.c
+++ b/dataformats.c
@@ -97,6 +97,26 @@ int fromhexstr(unsigned char *dstBinary, const char *srcHex, size_t nbinary)
   return (fromhex(dstBinary, srcHex, nbinary) == nbinary && srcHex[nbinary * 2] == '\0') ? 0 : -1;
 }
 
+int str_is_subscriber_id(const char *sid)
+{
+  return strcasecmp(sid, "broadcast") == 0 || _is_xstring(sid, SID_STRLEN);
+}
+
+int strn_is_subscriber_id(const char *sid, size_t *lenp)
+{
+  if (strncasecmp(sid, "broadcast", 9) == 0) {
+    if (lenp)
+      *lenp = 9;
+    return 1;
+  }
+  if (_is_xsubstring(sid, SID_STRLEN)) {
+    if (lenp)
+      *lenp = SID_STRLEN;
+    return 1;
+  }
+  return 0;
+}
+
 int rhizome_strn_is_manifest_id(const char *id)
 {
   return _is_xsubstring(id, RHIZOME_MANIFEST_ID_STRLEN);
@@ -214,32 +234,6 @@ int extractSid(const unsigned char *packet, int *ofs, char *sid)
   return 0;
 }
 
-int validateSid(const char *sid)
-{
-  if (!sid) {
-    WHY("invalid SID == NULL");
-    return 0;
-  }
-  if (strcasecmp(sid, "broadcast") == 0)
-    return 1;
-  const char *s = sid;
-  const char *e = sid + SID_STRLEN;
-  while (s != e && isxdigit(*s))
-    ++s;
-  if (s != e) {
-    if (*s)
-      WHYF("invalid SID, contains non-hex character 0x%02x at offset %d", *s, s - sid);
-    else
-      WHYF("invalid SID, too short (strlen %d)", s - sid);
-    return 0;
-  }
-  if (*s) {
-    WHYF("invalid SID, too long");
-    return 0;
-  }
-  return 1;
-}
-
 int stowSid(unsigned char *packet, int ofs, const char *sid)
 {
   if (debug & DEBUG_PACKETFORMATS)
diff --git a/rhizome.c b/rhizome.c
index ec6acf10..83042382 100644
--- a/rhizome.c
+++ b/rhizome.c
@@ -130,16 +130,17 @@ int rhizome_manifest_check_sanity(rhizome_manifest *m_in)
   } else if (strcasecmp(service, RHIZOME_SERVICE_MESHMS) == 0) {
     if (sender == NULL || !sender[0])
       return WHY("MeshMS Manifest missing 'sender' field");
-    if (!validateSid(sender))
-      return WHY("MeshMS Manifest contains invalid 'sender' field");
+    if (!str_is_subscriber_id(sender))
+      return WHYF("MeshMS Manifest contains invalid 'sender' field: %s", sender);
     if (recipient == NULL || !recipient[0])
       return WHY("MeshMS Manifest missing 'recipient' field");
-    if (!validateSid(recipient))
-      return WHY("MeshMS Manifest contains invalid 'recipient' field");
+    if (!str_is_subscriber_id(recipient))
+      return WHYF("MeshMS Manifest contains invalid 'recipient' field: %s", recipient);
   } else {
     return WHY("Invalid service type");
   }
-  if (debug & DEBUG_RHIZOME) DEBUGF("sender='%s'", sender ? sender : "(null)");
+  if (debug & DEBUG_RHIZOME)
+    DEBUGF("sender='%s'", sender ? sender : "(null)");
 
   /* passes all sanity checks */
   return 0;
diff --git a/serval.h b/serval.h
index 45f81c29..eac2fac5 100755
--- a/serval.h
+++ b/serval.h
@@ -685,7 +685,9 @@ int fromhexstr(unsigned char *dstBinary, const char *srcHex, size_t bytes);
 int hexvalue(char c);
 char *str_toupper_inplace(char *s);
 
-int validateSid(const char *sid);
+int str_is_subscriber_id(const char *sid);
+int strn_is_subscriber_id(const char *sid, size_t *lenp);
+
 int stowSid(unsigned char *packet, int ofs, const char *sid);
 int stowDid(unsigned char *packet,int *ofs,char *did);
 int isFieldZeroP(unsigned char *packet,int start,int count);