diff --git a/resources/functions/follow/follow.sql b/resources/functions/follow/follow.sql
index 3043f5d..a025d2d 100644
--- a/resources/functions/follow/follow.sql
+++ b/resources/functions/follow/follow.sql
@@ -1,19 +1,21 @@
-create or replace function follow(reference regclass, target_id uuid, citizen_id uuid) returns void
+create or replace function follow(reference regclass, _target_id uuid, _citizen_id uuid) returns void
     language plpgsql as
 $$
-declare
-    _citizen_id alias for citizen_id;
-    _target_id alias for target_id;
 begin
     if reference = 'article'::regclass then
         insert into follow_article (citizen_id, target_id)
-        values (_citizen_id, _target_id);
+        values (_citizen_id, _target_id)
+        on conflict (citizen_id, target_id) do nothing;
     elseif reference = 'constitution'::regclass then
         insert into follow_constitution (citizen_id, target_id)
-        values (_citizen_id, _target_id);
+        values (_citizen_id, _target_id)
+        on conflict (citizen_id, target_id) do nothing;
     elseif reference = 'citizen'::regclass then
         insert into follow_citizen (citizen_id, target_id)
-        values (_citizen_id, _target_id);
+        values (_citizen_id, _target_id)
+        on conflict (citizen_id, target_id) do nothing;
+    else
+        raise exception '% no implemented', reference::text;
     end if;
 end;
 $$;
diff --git a/resources/sql/migrations/0000-init_schema.up.sql b/resources/sql/migrations/0000-init_schema.up.sql
index cee2c62..0642b6f 100644
--- a/resources/sql/migrations/0000-init_schema.up.sql
+++ b/resources/sql/migrations/0000-init_schema.up.sql
@@ -193,7 +193,8 @@ create table extra
 create table follow
 (
     foreign key (citizen_id) references citizen (id),
-    primary key (id)
+    primary key (id),
+    unique (citizen_id, target_id)
 ) inherits (extra);
 
 create table follow_article
@@ -201,7 +202,8 @@ create table follow_article
     target_reference regclass default 'article'::regclass not null,
     foreign key (citizen_id) references citizen (id),
     foreign key (target_id) references article (id),
-    primary key (id)
+    primary key (id),
+    unique (citizen_id, target_id)
 ) inherits (follow);
 
 create table follow_constitution
@@ -209,7 +211,8 @@ create table follow_constitution
     target_reference regclass default 'constitution'::regclass not null,
     foreign key (citizen_id) references citizen (id),
     foreign key (target_id) references constitution (id),
-    primary key (id)
+    primary key (id),
+    unique (citizen_id, target_id)
 ) inherits (follow);
 
 create table follow_citizen
@@ -217,7 +220,8 @@ create table follow_citizen
     target_reference regclass default 'citizen'::regclass not null,
     foreign key (citizen_id) references citizen (id),
     foreign key (target_id) references citizen (id),
-    primary key (id)
+    primary key (id),
+    unique (citizen_id, target_id)
 ) inherits (follow);
 
 
diff --git a/resources/tests/comment.sql b/resources/tests/comment.sql
index 677874b..b972081 100644
--- a/resources/tests/comment.sql
+++ b/resources/tests/comment.sql
@@ -57,7 +57,7 @@ begin
     assert (select count(*) = 1 from "comment"), 'edit comment must not insert new comment';
     assert (select count(*) = 1 from "comment" where content = 'edited'), 'edit comment must not insert new comment';
 
-    -- delete article and context
+    -- delete comment and context
     delete from "comment";
     delete from article;
     delete from citizen;
diff --git a/resources/tests/follow.sql b/resources/tests/follow.sql
index 2a8ba3d..6c84a38 100644
--- a/resources/tests/follow.sql
+++ b/resources/tests/follow.sql
@@ -38,13 +38,16 @@ begin
     _citizen_id2 := created_citizen2->>'id';
 
 
+    perform follow('citizen'::regclass, _citizen_id, _citizen_id2);
+    assert (select count(*) > 0 from follow), 'follow must be inserted';
+
     perform follow('citizen'::regclass, _citizen_id, _citizen_id2);
     assert (select count(*) > 0 from follow), 'follow must be inserted';
 
     perform unfollow('citizen'::regclass, _citizen_id, _citizen_id2);
     assert (select count(*) = 0 from follow), 'follow must be deleted after unfollow';
 
-    -- delete article and context
+    -- delete follow and context
     delete from citizen;
     delete from "user";