diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index 070a591..03dc2d4 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -157,7 +157,7 @@
         return( 1 );
 
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
-    if( conf->psk_opaque != 0 )
+    if( ! psa_key_handle_is_null( conf->psk_opaque ) )
         return( 1 );
 #endif /* MBEDTLS_USE_PSA_CRYPTO */
 
@@ -172,13 +172,13 @@
         /* If we've used a callback to select the PSK,
          * the static configuration is irrelevant. */
 
-        if( ssl->handshake->psk_opaque != 0 )
+        if( ! psa_key_handle_is_null( ssl->handshake->psk_opaque ) )
             return( 1 );
 
         return( 0 );
     }
 
-    if( ssl->conf->psk_opaque != 0 )
+    if( ! psa_key_handle_is_null( ssl->conf->psk_opaque ) )
         return( 1 );
 
     return( 0 );