diff --git a/src/unit-test-coverage/shared/src/coveragetest-dir.c b/src/unit-test-coverage/shared/src/coveragetest-dir.c
index d197136a0..a6ea62bc1 100644
--- a/src/unit-test-coverage/shared/src/coveragetest-dir.c
+++ b/src/unit-test-coverage/shared/src/coveragetest-dir.c
@@ -70,7 +70,11 @@ void Test_OS_DirectoryOpen(void)
     UtAssert_True(actual == expected, "OS_DirectoryOpen() (%ld) == OS_SUCCESS", (long)actual);
     OSAPI_TEST_OBJID(objid, !=, OS_OBJECT_ID_UNDEFINED);
 
-    OSAPI_TEST_FUNCTION_RC(OS_DirectoryOpen(NULL, NULL), OS_INVALID_POINTER);
+    /*
+     * Note that the second arg (path) is validated by a separate unit (OS_TranslatePath),
+     * so it should not be passed NULL here
+     */
+    OSAPI_TEST_FUNCTION_RC(OS_DirectoryOpen(NULL, "Dir"), OS_INVALID_POINTER);
 }
 
 void Test_OS_DirectoryClose(void)
diff --git a/src/unit-tests/osfile-test/ut_osfile_dirio_test.c b/src/unit-tests/osfile-test/ut_osfile_dirio_test.c
index a71fd90c8..b6ed6d5a4 100644
--- a/src/unit-tests/osfile-test/ut_osfile_dirio_test.c
+++ b/src/unit-tests/osfile-test/ut_osfile_dirio_test.c
@@ -284,6 +284,7 @@ void UT_os_closedir_test()
     os_dirent_t dirEntry;
 
     UT_RETVAL(OS_DirectoryClose(UT_OBJID_INCORRECT), OS_ERR_INVALID_ID);
+    UT_RETVAL(OS_DirectoryClose(OS_OBJECT_ID_UNDEFINED), OS_ERR_INVALID_ID);
 
     /*-----------------------------------------------------*/
     /* #2 Nominal */
@@ -358,6 +359,7 @@ void UT_os_readdir_test()
     /* Invalid ID */
 
     UT_RETVAL(OS_DirectoryRead(UT_OBJID_INCORRECT, &dirent), OS_ERR_INVALID_ID);
+    UT_RETVAL(OS_DirectoryRead(OS_OBJECT_ID_UNDEFINED, &dirent), OS_ERR_INVALID_ID);
 
     /*-----------------------------------------------------*/
     /* #3 Nominal */
@@ -449,6 +451,7 @@ void UT_os_rewinddir_test()
     /* Invalid ID */
 
     UT_RETVAL(OS_DirectoryRewind(UT_OBJID_INCORRECT), OS_ERR_INVALID_ID);
+    UT_RETVAL(OS_DirectoryRewind(OS_OBJECT_ID_UNDEFINED), OS_ERR_INVALID_ID);
 
     /*-----------------------------------------------------*/
     /* #2 Nominal */