diff --git a/static_core/plugins/ets/tests/ets-templates/07.expressions/11.function_call_expression/fcall.params.yaml b/static_core/plugins/ets/tests/ets-templates/07.expressions/11.function_call_expression/fcall.params.yaml
index 50b3f1b6224549eb87a6bb7cc758c7cbc45ccdf6..d21323afc8c2f07ba6e6f4a8a53ba46f56b9bb57 100644
--- a/static_core/plugins/ets/tests/ets-templates/07.expressions/11.function_call_expression/fcall.params.yaml
+++ b/static_core/plugins/ets/tests/ets-templates/07.expressions/11.function_call_expression/fcall.params.yaml
@@ -216,7 +216,7 @@ cases:
         let r: Boolean | undefined = ll?.('Hello', 42, true)
         arktest.assertEQ(undefined, r)
         arktest.assertEQ(0, calls)
-        
+
         ll = getLambdaOrNull(true)
         r = ll?.('Hello', 42, true)
         arktest.assertEQ(true, r)
@@ -294,3 +294,10 @@ cases:
         let value = ((up: LP): User => { return up() }) () { return {name: 'Alice', age: 16 } }
         arktest.assertEQ('Alice', value.name)
         arktest.assertTrue(value instanceof User)
+
+    - decl: |-
+        function bar(callee: (a: int) => void): void {
+          callee(1)
+        }
+      use: |-
+        bar((): void => {})
diff --git a/static_core/plugins/ets/tests/ets-templates/16.concurrency/03.asynchronous_api/05.promise/p.params.yaml b/static_core/plugins/ets/tests/ets-templates/16.concurrency/03.asynchronous_api/05.promise/p.params.yaml
index 5ed304c6a0b6ef17d25b677d2ed27b67f2c79fec..1621d83e6fc1c8943ff909f0dcc398eb8383703e 100644
--- a/static_core/plugins/ets/tests/ets-templates/16.concurrency/03.asynchronous_api/05.promise/p.params.yaml
+++ b/static_core/plugins/ets/tests/ets-templates/16.concurrency/03.asynchronous_api/05.promise/p.params.yaml
@@ -14,12 +14,11 @@
 ---
 cases:
     - decl: |-
-          type ON = Object|null
           let s = 'XYZ'
       use: |-
           // test resolving path
           let r: Promise<string> = new Promise<string>(
-              (resolve: (p: string) => void, reject: (p: ON) => void): void => {
+              (resolve: (p: string) => void, reject: (p: Error) => void): void => {
                   if (s == 'XYZ') {
                       resolve(s)
                   } else {
@@ -30,12 +29,11 @@ cases:
           arktest.assertTrue((await r) == 'XYZ')
 
     - decl: |-
-          type ON = Object|null
           let s = 'XYZ'
       use: |-
           // test rejection path
           let r: Promise<string> = new Promise<string>(
-              (resolve: (p: string) => void, reject: (p: ON) => void): void => {
+              (resolve: (p: string) => void, reject: (p: Error) => void): void => {
                   if (s != 'XYZ') {
                       resolve(s)
                   } else {
@@ -53,12 +51,11 @@ cases:
           arktest.assertTrue(false)
 
     - decl: |-
-          type ON = Object|null
           let s = 'XYZ'
       use: |-
           // test throw from resolving path
           let r: Promise<string> = new Promise<string>(
-              (resolve: (p: string) => void, reject: (p: ON) => void): void => {
+              (resolve: (p: string) => void, reject: (p: Error) => void): void => {
                   if (s == 'XYZ') {
                       throw new Error(s)
                   } else {
@@ -76,12 +73,11 @@ cases:
           arktest.assertTrue(false)
 
     - decl: |-
-          type ON = Object|null
           let initVal: number = 1.0
       use: |-
           // test then chain, resolved
           let r = new Promise<number>(
-              (resolve: (p: number) => void, reject: (p: ON) => void): void => {
+              (resolve: (p: number) => void, reject: (p: Error) => void): void => {
                   if (initVal > 0) {
                       resolve(initVal)
                   } else {
@@ -105,7 +101,7 @@ cases:
       use: |-
           // test catch chain
           let r: Promise<string|number> = new Promise<number>(
-              (resolve: (p: number) => void, reject: (p: ON) => void): void => {
+              (resolve: (p: number) => void, reject: (p: Error) => void): void => {
                   if (initVal < 0) {
                       resolve(initVal)
                   } else {
@@ -144,7 +140,7 @@ cases:
       use: |-
           // test mixed then and catch chain
           let r: Promise<string> = new Promise<string>(
-              (resolve: (p: string) => void, reject: (p: ON) => void): void => {
+              (resolve: (p: string) => void, reject: (p: Error) => void): void => {
                   if (initVal > 0) {
                       resolve('A')
                   } else {
diff --git a/static_core/plugins/ets/tests/interop_js/eacoro/eaworker_test.ets b/static_core/plugins/ets/tests/interop_js/eacoro/eaworker_test.ets
index 0ce3e701d043e6f001f20c0be0c6c279155401fe..b1d748ab5a992eca8ef7350d8bff9df989b93679 100644
--- a/static_core/plugins/ets/tests/interop_js/eacoro/eaworker_test.ets
+++ b/static_core/plugins/ets/tests/interop_js/eacoro/eaworker_test.ets
@@ -68,7 +68,7 @@ function RunTasksWithJsAsyncCallTest(): void {
         let modified = false;
         let method = JSRuntime.getPropertyJSValue(module, 'asyncWithAwait');
         let promise = (ESValue.wrap(JSRuntime.invoke(module, method))).toPromise();
-        let promise1 = promise.then((x:Object): void => {
+        let promise1 = promise.then((x:Any): void => {
             modified = true;
         });
 
diff --git a/static_core/plugins/ets/tests/interop_js/tests/promise/promise_tests.ets b/static_core/plugins/ets/tests/interop_js/tests/promise/promise_tests.ets
index 22bbdc25f8d7a91fd837c53167092b3304b3ad73..02a7fbf23293b4532d6cfeae2e42d9f8ee692a61 100644
--- a/static_core/plugins/ets/tests/interop_js/tests/promise/promise_tests.ets
+++ b/static_core/plugins/ets/tests/interop_js/tests/promise/promise_tests.ets
@@ -755,9 +755,11 @@ function testPromiseRaceRejected(): void {
 
 function testPromiseThenOnRejection(): void {
     globalTest = new Test();
-    Promise.reject<Error>(new Error("test")).then<void, string>(
-    (value: Object): void => {
+    Promise.reject<Error>(new Error("test")).then<string, string>(
+    (value: Object): string => {
         globalTest!.fail();
+        // String return type needed, until 'String|void' type is supported
+        return "";
     }, (error: Error): string => {
         return "correct flow";
     }).then<string, void>((value): string => {