diff --git a/marshmallow/schema.py b/marshmallow/schema.py
index <HASH>..<HASH> 100644
--- a/marshmallow/schema.py
+++ b/marshmallow/schema.py
@@ -766,6 +766,8 @@ class BaseSchema(base.SchemaABC):
             try:
                 field_obj = self.fields[field_name]
             except KeyError:
+                if field_name in self.declared_fields:
+                    return
                 raise ValueError('"{0}" field does not exist.'.format(field_name))
 
             if many:
Ignore field validator if field is declared but not in "only"