diff --git a/src/fr/anssi/smartpgp/SmartPGPApplet.java b/src/fr/anssi/smartpgp/SmartPGPApplet.java
index 66d7916..5d8af9c 100644
--- a/src/fr/anssi/smartpgp/SmartPGPApplet.java
+++ b/src/fr/anssi/smartpgp/SmartPGPApplet.java
@@ -433,6 +433,12 @@ public final class SmartPGPApplet extends Applet {
 
         case Constants.TAG_CARDHOLDER_CERTIFICATE:
             k = currentTagOccurenceToKey();
+
+            if(k == null) {
+                ISOException.throwIt(Constants.SW_REFERENCE_DATA_NOT_FOUND);
+                return 0;
+            }
+
             off = Util.arrayCopyNonAtomic(k.certificate, (short)0,
                                           buf, off,
                                           k.certificate_length);
@@ -461,6 +467,11 @@ public final class SmartPGPApplet extends Applet {
 
         final PGPKey k = currentTagOccurenceToKey();
 
+        if(k == null) {
+            ISOException.throwIt(Constants.SW_REFERENCE_DATA_NOT_FOUND);
+            return 0;
+        }
+
         transients.setCurrentTagOccurrence((byte)(transients.currentTagOccurrence() + 1));
 
         return Util.arrayCopyNonAtomic(k.certificate, (short)0,
@@ -774,6 +785,8 @@ public final class SmartPGPApplet extends Applet {
 
         final byte[] buf = transients.buffer;
 
+        PGPKey k = null;
+
         if(isOdd) {
 
             assertAdmin();
@@ -800,8 +813,6 @@ public final class SmartPGPApplet extends Applet {
                 return;
             }
 
-            PGPKey k = null;
-
             switch(Util.getShort(buf, off)) {
             case Constants.CRT_SIGNATURE_KEY:
                 k = data.pgp_keys[Persistent.PGP_KEYS_OFFSET_SIG];
@@ -1005,7 +1016,12 @@ public final class SmartPGPApplet extends Applet {
 
             case Constants.TAG_CARDHOLDER_CERTIFICATE:
                 assertAdmin();
-                currentTagOccurenceToKey().setCertificate(buf, (short)0, lc);
+                k = currentTagOccurenceToKey();
+                if(k == null) {
+                    ISOException.throwIt(Constants.SW_REFERENCE_DATA_NOT_FOUND);
+                    return;
+                }
+                k.setCertificate(buf, (short)0, lc);
                 break;
 
             case Constants.TAG_ALGORITHM_ATTRIBUTES_SIG: