diff --git a/src/business/business-ledger/gncEntryLedger.c b/src/business/business-ledger/gncEntryLedger.c
index f80231d112..ba9dbced3c 100644
--- a/src/business/business-ledger/gncEntryLedger.c
+++ b/src/business/business-ledger/gncEntryLedger.c
@@ -426,7 +426,7 @@ static void create_invoice_query (GncEntryLedger *ledger)
      *          ( Entry->Billable == TRUE AND
      *            Entry->Bill->Is-Posted? == TRUE AND
      *            ( Entry->BillTo == Invoice->parent OR
-     *              Entry->Bill->BillTo == Invoice->parent ) )
+     *              ( Entry->BillTo == NULL AND Entry->Bill->BillTo == Invoice->parent ) ) )
      *           OR
      *           ( Entry->Order->real-parent == Invoice->parent ) )
      * #endif
diff --git a/src/libqof/qof/qofquerycore.c b/src/libqof/qof/qofquerycore.c
index 97be12c2ab..8fa2109e73 100644
--- a/src/libqof/qof/qofquerycore.c
+++ b/src/libqof/qof/qofquerycore.c
@@ -730,7 +730,9 @@ qof_query_guid_predicate (QofGuidMatch options, GList *guid_list)
     query_guid_t pdata;
     GList *node;
 
-    if (NULL == guid_list) return NULL;
+    /* An empty list of guids is only valid when testing for a null GUID value */
+    if (!guid_list)
+        g_return_val_if_fail (options == QOF_GUID_MATCH_NULL, NULL);
 
     pdata = g_new0 (query_guid_def, 1);
     pdata->pd.how = QOF_COMPARE_EQUAL;