diff --git a/bin/tools/yaml_import.py b/bin/tools/yaml_import.py
index 8868d153ebf..814779b3f36 100644
--- a/bin/tools/yaml_import.py
+++ b/bin/tools/yaml_import.py
@@ -70,14 +70,16 @@ def is_url(node):
 
 def is_eval(node):
     return isinstance(node, yaml_tag.Eval)
-    
+
 def is_ref(node):
     return isinstance(node, yaml_tag.Ref) \
         or _is_yaml_mapping(node, yaml_tag.Ref)
-    
+
 def is_ir_set(node):
     return _is_yaml_mapping(node, yaml_tag.IrSet)
 
+def is_string(node):
+    return isinstance(node, basestring)
 
 class TestReport(object):
     def __init__(self):
@@ -374,12 +376,12 @@ class YamlInterpreter(object):
         elif column._type == "many2many":
             ids = [self.get_id(xml_id) for xml_id in expression]
             value = [(6, 0, ids)]
-        elif column._type == "date":
-            # enforce ISO format for date values, to be locale-agnostic during tests
+        elif column._type == "date" and is_string(expression):
+            # enforce ISO format for string date values, to be locale-agnostic during tests
             time.strptime(expression, misc.DEFAULT_SERVER_DATE_FORMAT)
             value = expression
-        elif column._type == "datetime":
-            # enforce ISO format for datetime values, to be locale-agnostic during tests
+        elif column._type == "datetime" and is_string(expression):
+            # enforce ISO format for string datetime values, to be locale-agnostic during tests
             time.strptime(expression, misc.DEFAULT_SERVER_DATETIME_FORMAT)
             value = expression
         else: # scalar field