diff --git a/modules/purchase/purchase.py b/modules/purchase/purchase.py
index 9eddc8430d..1e6ca9a29c 100644
--- a/modules/purchase/purchase.py
+++ b/modules/purchase/purchase.py
@@ -2223,7 +2223,8 @@ class ModifyHeader(Wizard):
                     value = str(value)
                 else:
                     value = value.id
-            elif isinstance(value, (list, tuple)):
+            elif (value and isinstance(value, (list, tuple))
+                    and isinstance(value[0], Model)):
                 value = [r.id for r in value]
             values[fieldname] = value
 
diff --git a/modules/sale/sale.py b/modules/sale/sale.py
index 6df33a7e93..e030330b11 100644
--- a/modules/sale/sale.py
+++ b/modules/sale/sale.py
@@ -2294,7 +2294,8 @@ class ModifyHeader(Wizard):
                     value = str(value)
                 else:
                     value = value.id
-            elif isinstance(value, (list, tuple)):
+            elif (value and isinstance(value, (list, tuple))
+                    and isinstance(value[0], Model)):
                 value = [r.id for r in value]
             values[fieldname] = value