diff --git a/src/etapi/attachments.js b/src/etapi/attachments.ts
similarity index 81%
rename from src/etapi/attachments.js
rename to src/etapi/attachments.ts
index 6ea042db1..258b9a186 100644
--- a/src/etapi/attachments.js
+++ b/src/etapi/attachments.ts
@@ -1,11 +1,13 @@
-const becca = require('../becca/becca');
-const eu = require('./etapi_utils');
-const mappers = require('./mappers');
-const v = require('./validators');
-const utils = require('../services/utils');
+import becca = require('../becca/becca');
+import eu = require('./etapi_utils');
+import mappers = require('./mappers');
+import v = require('./validators');
+import utils = require('../services/utils');
+import { Router } from 'express';
+import { AttachmentRow } from '../becca/entities/rows';
 
-function register(router) {
-    const ALLOWED_PROPERTIES_FOR_CREATE_ATTACHMENT = {
+function register(router: Router) {
+    const ALLOWED_PROPERTIES_FOR_CREATE_ATTACHMENT: ValidatorMap = {
         'ownerId': [v.notNull, v.isNoteId],
         'role': [v.notNull, v.isString],
         'mime': [v.notNull, v.isString],
@@ -15,17 +17,20 @@ function register(router) {
     };
 
     eu.route(router, 'post', '/etapi/attachments', (req, res, next) => {
-        const params = {};
-
-        eu.validateAndPatch(params, req.body, ALLOWED_PROPERTIES_FOR_CREATE_ATTACHMENT);
+        const _params: Partial<AttachmentRow> = {};
+        eu.validateAndPatch(_params, req.body, ALLOWED_PROPERTIES_FOR_CREATE_ATTACHMENT);
+        const params = _params as AttachmentRow;
 
         try {
+            if (!params.ownerId) {
+                throw new Error("Missing owner ID.");
+            }
             const note = becca.getNoteOrThrow(params.ownerId);
             const attachment = note.saveAttachment(params);
 
             res.status(201).json(mappers.mapAttachmentToPojo(attachment));
         }
-        catch (e) {
+        catch (e: any) {
             throw new eu.EtapiError(500, eu.GENERIC_CODE, e.message);
         }
     });
diff --git a/src/etapi/etapi-interface.ts b/src/etapi/etapi-interface.ts
new file mode 100644
index 000000000..b53d983dd
--- /dev/null
+++ b/src/etapi/etapi-interface.ts
@@ -0,0 +1,5 @@
+type ValidatorArg = object | undefined | null;
+
+type ValidatorFunc = (obj: ValidatorArg) => (string | undefined);
+
+type ValidatorMap = Record<string, ValidatorFunc[]>;
\ No newline at end of file
diff --git a/src/etapi/etapi_utils.ts b/src/etapi/etapi_utils.ts
index f7678b81f..4880bed86 100644
--- a/src/etapi/etapi_utils.ts
+++ b/src/etapi/etapi_utils.ts
@@ -120,7 +120,7 @@ function getAndCheckAttribute(attributeId: string) {
     }
 }
 
-function validateAndPatch(target: Record<string, string>, source: Record<string, string>, allowedProperties: Record<string, ((value: string) => boolean)[]>) {
+function validateAndPatch(target: any, source: any, allowedProperties: ValidatorMap) {
     for (const key of Object.keys(source)) {
         if (!(key in allowedProperties)) {
             throw new EtapiError(400, "PROPERTY_NOT_ALLOWED", `Property '${key}' is not allowed for this method.`);
diff --git a/src/etapi/validators.ts b/src/etapi/validators.ts
index 7119a5319..485bd8d33 100644
--- a/src/etapi/validators.ts
+++ b/src/etapi/validators.ts
@@ -1,19 +1,19 @@
 import noteTypeService = require('../services/note_types');
 import dateUtils = require('../services/date_utils');
 
-function mandatory(obj: any | undefined) {
+function mandatory(obj: ValidatorArg) {
     if (obj === undefined) {
         return `mandatory, but not set`;
     }
 }
 
-function notNull(obj: any | null) {
+function notNull(obj: ValidatorArg) {
     if (obj === null) {
         return `cannot be null`;
     }
 }
 
-function isString(obj: object | undefined | null) {
+function isString(obj: ValidatorArg) {
     if (obj === undefined || obj === null) {
         return;
     }
@@ -23,7 +23,7 @@ function isString(obj: object | undefined | null) {
     }
 }
 
-function isLocalDateTime(obj: object | undefined | null) {
+function isLocalDateTime(obj: ValidatorArg) {
     if (obj === undefined || obj === null || typeof obj !== "string") {
         return;
     }
@@ -31,7 +31,7 @@ function isLocalDateTime(obj: object | undefined | null) {
     return dateUtils.validateLocalDateTime(obj);
 }
 
-function isUtcDateTime(obj: object | undefined | null) {
+function isUtcDateTime(obj: ValidatorArg) {
     if (obj === undefined || obj === null || typeof obj !== "string") {
         return;
     }
@@ -39,7 +39,7 @@ function isUtcDateTime(obj: object | undefined | null) {
     return dateUtils.validateUtcDateTime(obj);
 }
 
-function isBoolean(obj: object | undefined | null) {
+function isBoolean(obj: ValidatorArg) {
     if (obj === undefined || obj === null) {
         return;
     }
@@ -49,7 +49,7 @@ function isBoolean(obj: object | undefined | null) {
     }
 }
 
-function isInteger(obj: object | undefined | null) {
+function isInteger(obj: ValidatorArg) {
     if (obj === undefined || obj === null) {
         return;
     }
@@ -59,7 +59,7 @@ function isInteger(obj: object | undefined | null) {
     }
 }
 
-function isNoteId(obj: object | undefined | null) {
+function isNoteId(obj: ValidatorArg) {
     if (obj === undefined || obj === null) {
         return;
     }
@@ -75,7 +75,7 @@ function isNoteId(obj: object | undefined | null) {
     }
 }
 
-function isNoteType(obj: object | undefined | null) {
+function isNoteType(obj: ValidatorArg) {
     if (obj === undefined || obj === null) {
         return;
     }
@@ -87,7 +87,7 @@ function isNoteType(obj: object | undefined | null) {
     }
 }
 
-function isAttributeType(obj: object | undefined | null) {
+function isAttributeType(obj: ValidatorArg) {
     if (obj === undefined || obj === null) {
         return;
     }
@@ -97,7 +97,7 @@ function isAttributeType(obj: object | undefined | null) {
     }
 }
 
-function isValidEntityId(obj: object | undefined | null) {
+function isValidEntityId(obj: ValidatorArg) {
     if (obj === undefined || obj === null) {
         return;
     }
diff --git a/src/routes/routes.js b/src/routes/routes.js
index 182639b84..a264f3c5b 100644
--- a/src/routes/routes.js
+++ b/src/routes/routes.js
@@ -63,7 +63,7 @@ const shareRoutes = require('../share/routes.js');
 
 const etapiAuthRoutes = require('../etapi/auth.js');
 const etapiAppInfoRoutes = require('../etapi/app_info');
-const etapiAttachmentRoutes = require('../etapi/attachments.js');
+const etapiAttachmentRoutes = require('../etapi/attachments');
 const etapiAttributeRoutes = require('../etapi/attributes');
 const etapiBranchRoutes = require('../etapi/branches.js');
 const etapiNoteRoutes = require('../etapi/notes.js');