diff --git a/doc/crypto/RSA_check_key.pod b/doc/crypto/RSA_check_key.pod
index 5737ecdc3e286b57c2b977a12e1f36ef02fa66cf..3d824a07f570130f158c0e7e569e5ac5e9dc7d04 100644
--- a/doc/crypto/RSA_check_key.pod
+++ b/doc/crypto/RSA_check_key.pod
@@ -18,7 +18,9 @@ in fact prime, and that B<n = p*q>.
 It also checks that B<d*e = 1 mod (p-1*q-1)>,
 and that B<dmp1>, B<dmq1> and B<iqmp> are set correctly or are B<NULL>.
 
-The key's public components may not be B<NULL>.
+As such, this function can not be used with any arbitrary RSA key object,
+even if it is otherwise fit for regular RSA operation. See B<NOTES> for more
+information.
 
 =head1 RETURN VALUE
 
@@ -30,12 +32,29 @@ obtained using L<ERR_get_error(3)|ERR_get_error(3)>.
 
 =head1 NOTES
 
-RSA_check_key() can only check soft keys.  If given hard keys, i.e. keys
-that were retreived from an ENGINE (with ENGINE_load_private_key()),
-RSA_check_key() will always return 0, as if the key was invalid.  The
-reason is that the private components B<p>, B<q> and B<d> are normally
-not available to OpenSSL for hard keys, and the checks can therefore not
-be done.
+This function does not work on RSA public keys that have only the modulus
+and public exponent elements populated. It performs integrity checks on all
+the RSA key material, so the RSA key structure must contain all the private
+key data too.
+
+Unlike most other RSA functions, this function does B<not> work
+transparently with any underlying ENGINE implementation because it uses the
+key data in the RSA structure directly. An ENGINE implementation can
+override the way key data is stored and handled, and can even provide
+support for HSM keys - in which case the RSA structure may contain B<no>
+key data at all! If the ENGINE in question is only being used for
+acceleration or analysis purposes, then in all likelihood the RSA key data
+is complete and untouched, but this can't be assumed in the general case.
+
+=head1 BUGS
+
+A method of verifying the RSA key using opaque RSA API functions might need
+to be considered. Right now RSA_check_key() simply uses the RSA structure
+elements directly, bypassing the RSA_METHOD table altogether (and
+completely violating encapsulation and object-orientation in the process).
+The best fix will probably be to introduce a "check_key()" handler to the
+RSA_METHOD function table so that alternative implementations can also
+provide their own verifiers.
 
 =head1 SEE ALSO