diff --git a/library/pem.c b/library/pem.c
index 3e3e96d..3f6d330 100644
--- a/library/pem.c
+++ b/library/pem.c
@@ -333,21 +333,12 @@
 #endif /* POLARSSL_AES_C */
 
         /*
-         * The result should look like RSAPrivateKey or ECPrivateKey
-         * We use the following heuristic:
-         *    len must be more than 6
-         *    byte 1 must be 0x30 (SEQUENCE tag)
-         *    then allow for one to 3 length bytes
-         *    then we must have 0x02 0x01 (INTEGER tag + length, for version)
-         *    version must be less than 4 (leaves some room)
+         * The result will be ASN.1 starting with a SEQUENCE tag, with 1 to 3
+         * length bytes (allow 4 to be sure) in all known use cases.
+         *
+         * Use that as heurisitic to try detecting password mismatchs.
          */
-        if( ! ( len > 6 && buf[0] == 0x30 && (
-                   ( buf[1] <= 0x7f && /* 1 length byte */
-                     buf[2] == 0x02 && buf[3] == 0x01 && buf[4] < 4 ) ||
-                   ( buf[1] == 0x81 && /* 2 length bytes */
-                     buf[3] == 0x02 && buf[4] == 0x01 && buf[5] < 4 ) ||
-                   ( buf[1] == 0x82 && /* 2 length bytes */
-                     buf[4] == 0x02 && buf[5] == 0x01 && buf[6] < 4 ) ) ) )
+        if( len <= 2 || buf[0] != 0x30 || buf[1] > 0x83 )
         {
             polarssl_free( buf );
             return( POLARSSL_ERR_PEM_PASSWORD_MISMATCH );