diff --git a/src/Model/Migration.hs b/src/Model/Migration.hs
index df6289f1f..6b4c67ee8 100644
--- a/src/Model/Migration.hs
+++ b/src/Model/Migration.hs
@@ -140,23 +140,31 @@ getMissingMigrations = do
 
 
 migrateManual :: Migration
-migrateManual =
-  addMigrations
-    [ (False, "CREATE INDEX IF NOT EXISTS course_application_file_content ON course_application_file (content)")
-    , (False, "CREATE INDEX IF NOT EXISTS material_file_content ON material_file (content)")
-    , (False, "CREATE INDEX IF NOT EXISTS course_news_file_content ON course_news_file (content)")
-    , (False, "CREATE INDEX IF NOT EXISTS sheet_file_content ON sheet_file (content)")
-    , (False, "CREATE INDEX IF NOT EXISTS course_app_instruction_file_content ON course_app_instruction_file (content)")
-    , (False, "CREATE INDEX IF NOT EXISTS allocation_matching_log ON allocation_matching (log)")
-    , (False, "CREATE INDEX IF NOT EXISTS submission_file_content ON submission_file (content)")
-    , (False, "CREATE INDEX IF NOT EXISTS session_file_content ON session_file (content)")
-    , (False, "CREATE INDEX IF NOT EXISTS file_lock_content ON file_lock (content)")
-    , (False, "CREATE INDEX IF NOT EXISTS user_lower_display_email ON \"user\" (lower(display_email))")
-    , (False, "CREATE INDEX IF NOT EXISTS user_lower_email ON \"user\" (lower(email))")
-    , (False, "CREATE INDEX IF NOT EXISTS user_lower_ident ON \"user\" (lower(ident))")
-    , (False, "CREATE INDEX IF NOT EXISTS submission_sheet ON submission (sheet)")
-    , (False, "CREATE INDEX IF NOT EXISTS submission_edit_submission ON submission_edit (submission)")
+migrateManual = do
+  mapM_ (uncurry addIndex)
+    [ ("course_application_file_content",     "CREATE INDEX course_application_file_content ON course_application_file (content)"        )
+    , ("material_file_content",               "CREATE INDEX material_file_content ON material_file (content)"                            )
+    , ("course_news_file_content",            "CREATE INDEX course_news_file_content ON course_news_file (content)"                      )
+    , ("sheet_file_content",                  "CREATE INDEX sheet_file_content ON sheet_file (content)"                                  )
+    , ("course_app_instruction_file_content", "CREATE INDEX course_app_instruction_file_content ON course_app_instruction_file (content)")
+    , ("allocation_matching_log",             "CREATE INDEX allocation_matching_log ON allocation_matching (log)"                        )
+    , ("submission_file_content",             "CREATE INDEX submission_file_content ON submission_file (content)"                        )
+    , ("session_file_content",                "CREATE INDEX session_file_content ON session_file (content)"                              )
+    , ("file_lock_content",                   "CREATE INDEX file_lock_content ON file_lock (content)"                                    )
+    , ("user_lower_display_email",            "CREATE INDEX user_lower_display_email ON \"user\" (lower(display_email))"                 )
+    , ("user_lower_email",                    "CREATE INDEX user_lower_email ON \"user\" (lower(email))"                                 )
+    , ("user_lower_ident",                    "CREATE INDEX user_lower_ident ON \"user\" (lower(ident))"                                 )
+    , ("submission_sheet",                    "CREATE INDEX submission_sheet ON submission (sheet)"                                      )
+    , ("submission_edit_submission",          "CREATE INDEX submission_edit_submission ON submission_edit (submission)"                  )
     ]
+  where
+    addIndex :: Text -> Sql -> Migration
+    addIndex ixName ixDef = do
+      res <- lift $ lift [sqlQQ|SELECT EXISTS (SELECT 1 FROM pg_indexes WHERE schemaname = current_schema() AND indexname = #{ixName})|]
+      alreadyDefined <- case res of
+        [Single e] -> return e
+        _other -> return True
+      unless alreadyDefined $ addMigration False ixDef
 
 
 {-