diff --git a/src/cssrlib/osnma.py b/src/cssrlib/osnma.py
index 9d98d41..689dba0 100644
--- a/src/cssrlib/osnma.py
+++ b/src/cssrlib/osnma.py
@@ -4,6 +4,9 @@
 [1] Galileo Open Service Navigation Message Authentication (OSNMA)
     Signal-in-Space Interface Control Document (SIS ICD), October, 2023.
 
+[2] Galileo Open Service Navigation Message Authentication (OSNMA)
+    Receiver Guidelines Issue 1.3, January, 2024.
+
 Note:
     to use the package for OSNMA, the user needs to
     install the public keys provided by EUSPA.
diff --git a/src/cssrlib/qznma.py b/src/cssrlib/qznma.py
index a6dc49e..e6c4853 100644
--- a/src/cssrlib/qznma.py
+++ b/src/cssrlib/qznma.py
@@ -572,6 +572,10 @@ def verify_gnss_nav(self, npr, mnav):
         if self.pk is None:
             pubk_path = self.pubk_bdir + f"/{npr.keyid:03d}.der"
             self.pk = load_pubkey(pubk_path)
+            if self.pk is None:
+                if self.monlevel > 0:
+                    print(f"loading public key {npr.keyid} was faild.")
+                return False
 
         ds_der = raw2der(npr.ds)
         status = False
@@ -762,6 +766,10 @@ def verify_qzss_nav(self, sat, npr, msg, mode):
         if self.pk is None:
             pubk_path = self.pubk_bdir + f"/{npr.keyid:03d}.der"
             self.pk = load_pubkey(pubk_path)
+            if self.pk is None:
+                if self.monlevel > 0:
+                    print(f"loading public key {npr.keyid} was faild.")
+                return False
 
         status = False
         try: