diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index d9d48708c..086403109 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -1227,7 +1227,7 @@ static psa_status_t psa_copy_key_material( const psa_key_slot_t *source,
     buffer_size = PSA_KEY_EXPORT_MAX_SIZE( source->type,
                                            psa_get_key_bits( source ) );
     buffer = mbedtls_calloc( 1, buffer_size );
-    if( buffer == NULL )
+    if( buffer == NULL && buffer_size != 0 )
         return( PSA_ERROR_INSUFFICIENT_MEMORY );
     status = psa_internal_export_key( source, buffer, buffer_size, &length, 0 );
     if( status != PSA_SUCCESS )