diff --git a/src/API.php b/src/API.php
index 1942a38..22063d2 100644
--- a/src/API.php
+++ b/src/API.php
@@ -198,7 +198,7 @@ final class API
 
 		$x = $this->execute('query',$parameters);
 
-		if ((! $x->QueryResponse) || (! $x->QueryResponse->Customer) || (count($x->QueryResponse->Customer) !== 1))
+		if ((! $x->QueryResponse) || (! object_get($x->QueryResponse,'Customer')) || (count($x->QueryResponse->Customer) !== 1))
 			throw new InvalidQueryResultException(sprintf('%s:Query response malformed',self::LOGKEY));
 
 		return new Customer($x->QueryResponse);
@@ -251,8 +251,8 @@ final class API
 
 		$x = $this->execute('query',$parameters);
 
-		if ((! $x->QueryResponse) || (! $x->QueryResponse->Invoice) || (count($x->QueryResponse->Invoice) !== 1))
-			throw new InvalidQueryResultException(sprintf('%s:Query response malformed',self::LOGKEY));
+		if ((! $x->QueryResponse) || (! object_get($x->QueryResponse,'Invoice')) || (count($x->QueryResponse->Invoice) !== 1))
+			throw new InvalidQueryResultException(sprintf('%s:Query response malformed [%s]',self::LOGKEY,serialize($x)));
 
 		return new Invoice($x->QueryResponse);
 	}