diff --git a/mylib/pgsql.py b/mylib/pgsql.py
index 9b7313f..606fc9e 100644
--- a/mylib/pgsql.py
+++ b/mylib/pgsql.py
@@ -225,12 +225,20 @@ class PgDB:
             )
 
         if isinstance(where_clauses, dict):
-            cls._combine_params(params, where_clauses)
+            sql_where_clauses = []
+            for field, value in where_clauses.items():
+                param = field
+                if field in params:
+                    idx = 1
+                    while param in params:
+                        param = '%s_%d' % (field, idx)
+                        idx += 1
+                cls._combine_params(params, {param: value})
+                sql_where_clauses.append(
+                    '"{field}" = %({param})s'.format(field=field, param=param)
+                )
             return (
-                (" %s " % where_op).join([
-                    '"{0}" = %({0})s'.format(key)
-                    for key in where_clauses
-                ]),
+                (" %s " % where_op).join(sql_where_clauses),
                 params
             )
         raise PgDBUnsupportedWHEREClauses(where_clauses)
diff --git a/tests/test_pgsql.py b/tests/test_pgsql.py
index 708739e..42b757f 100644
--- a/tests/test_pgsql.py
+++ b/tests/test_pgsql.py
@@ -212,6 +212,15 @@ def test_add_where_clauses_with_op():
         dict()
     )
 
+def test_add_where_clauses_with_duplicated_field():
+    sql="UPDATE table SET test1=%(test1)s"
+    params = dict(test1='new_value')
+    where_clauses = dict(test1='where_value')
+    assert PgDB._add_where_clauses(sql, params, where_clauses) == (
+        sql + ' WHERE "test1" = %(test1_1)s',
+        dict(test1='new_value', test1_1='where_value')
+    )
+
 def test_insert(mocker, test_pgdb):
     values = dict(test1=1, test2=2)
     mocker.patch(