diff --git a/scripts/pylib/twister/twisterlib/testplan.py b/scripts/pylib/twister/twisterlib/testplan.py
index 22c206dfa2c..d4031a96364 100755
--- a/scripts/pylib/twister/twisterlib/testplan.py
+++ b/scripts/pylib/twister/twisterlib/testplan.py
@@ -188,6 +188,8 @@ class TestPlan:
         num = self.add_testsuites(testsuite_filter=self.run_individual_testsuite)
         if num == 0:
             raise TwisterRuntimeError("No test cases found at the specified location...")
+        if self.load_errors:
+            raise TwisterRuntimeError(f"Found {self.load_errors} errors loading {num} test configurations.")
 
         self.find_subtests()
         # get list of scenarios we have parsed into one list
@@ -197,9 +199,6 @@ class TestPlan:
         self.report_duplicates()
         self.parse_configuration(config_file=self.env.test_config)
 
-        if self.load_errors:
-            raise TwisterRuntimeError("Errors while loading configurations")
-
         # handle quarantine
         ql = self.options.quarantine_list
         qv = self.options.quarantine_verify
@@ -605,10 +604,18 @@ class TestPlan:
                             suite.add_subcases(suite_dict, subcases, ztest_suite_names)
                         else:
                             suite.add_subcases(suite_dict)
+
                         if testsuite_filter:
                             scenario = os.path.basename(suite.name)
                             if suite.name and (suite.name in testsuite_filter or scenario in testsuite_filter):
                                 self.testsuites[suite.name] = suite
+                        elif suite.name in self.testsuites:
+                            msg = f"test suite '{suite.name}' in '{suite.yamlfile}' is already added"
+                            if suite.yamlfile == self.testsuites[suite.name].yamlfile:
+                                logger.debug(f"Skip - {msg}")
+                            else:
+                                msg = f"Duplicate {msg} from '{self.testsuites[suite.name].yamlfile}'"
+                                raise TwisterRuntimeError(msg)
                         else:
                             self.testsuites[suite.name] = suite
 
diff --git a/scripts/tests/twister/test_testplan.py b/scripts/tests/twister/test_testplan.py
index 0bf83ee9edb..a885d541f15 100644
--- a/scripts/tests/twister/test_testplan.py
+++ b/scripts/tests/twister/test_testplan.py
@@ -1309,19 +1309,35 @@ def test_testplan_get_all_tests():
 
 
 TESTDATA_9 = [
-    ([], False, 7),
-    ([], True, 5),
-    (['good_test/dummy.common.1', 'good_test/dummy.common.2', 'good_test/dummy.common.3'], False, 3),
-    (['good_test/dummy.common.1', 'good_test/dummy.common.2', 'good_test/dummy.common.3'], True, 0),
+    ([], False, True, 11, 1),
+    ([], False, False, 7, 2),
+    ([], True, False, 9, 1),
+    ([], True, True, 9, 1),
+    ([], True, False, 9, 1),
+    (['good_test/dummy.common.1', 'good_test/dummy.common.2', 'good_test/dummy.common.3'], False, True, 3, 1),
+    (['good_test/dummy.common.1', 'good_test/dummy.common.2',
+      'duplicate_test/dummy.common.1', 'duplicate_test/dummy.common.2'], False, True, 4, 1),
+    (['dummy.common.1', 'dummy.common.2'], False, False, 2, 1),
+    (['good_test/dummy.common.1', 'good_test/dummy.common.2', 'good_test/dummy.common.3'], True, True, 0, 1),
 ]
 
 @pytest.mark.parametrize(
-    'testsuite_filter, use_alt_root, expected_suite_count',
+    'testsuite_filter, use_alt_root, detailed_id, expected_suite_count, expected_errors',
     TESTDATA_9,
-    ids=['no testsuite filter', 'no testsuite filter, alt root',
-         'testsuite filter', 'testsuite filter, alt root']
+    ids=[
+        'no testsuite filter, detailed id',
+        'no testsuite filter, short id',
+        'no testsuite filter, alt root, detailed id',
+        'no filter, alt root, detailed id',
+        'no filter, alt root, short id',
+        'testsuite filter',
+        'testsuite filter and valid duplicate',
+        'testsuite filter, short id and duplicate',
+        'testsuite filter, alt root',
+    ]
 )
-def test_testplan_add_testsuites(tmp_path, testsuite_filter, use_alt_root, expected_suite_count):
+def test_testplan_add_testsuites(tmp_path, testsuite_filter, use_alt_root, detailed_id,
+                                 expected_errors, expected_suite_count):
     # tmp_path
     # ├ tests  <- test root
     # │ ├ good_test
@@ -1330,6 +1346,8 @@ def test_testplan_add_testsuites(tmp_path, testsuite_filter, use_alt_root, expec
     # │ │ └ testcase.yaml
     # │ ├ good_sample
     # │ │ └ sample.yaml
+    # │ ├ duplicate_test
+    # │ │ └ testcase.yaml
     # │ └ others
     # │   └ other.txt
     # └ other_tests  <- alternate test root
@@ -1381,6 +1399,25 @@ tests:
     samplefile_1 = tmp_good_sample_dir / 'sample.yaml'
     samplefile_1.write_text(samplecase_yaml_1)
 
+    tmp_duplicate_test_dir = tmp_test_root_dir / 'duplicate_test'
+    tmp_duplicate_test_dir.mkdir()
+    # The duplicate needs to have the same number of tests as these configurations
+    # can be read either with duplicate_test first, or good_test first, so number
+    # of selected tests needs to be the same in both situations.
+    testcase_yaml_4 = """\
+tests:
+  dummy.common.1:
+    build_on_all: true
+  dummy.common.2:
+    build_on_all: true
+  dummy.common.3:
+    build_on_all: true
+  dummy.special:
+    build_on_all: false
+"""
+    testfile_4 = tmp_duplicate_test_dir / 'testcase.yaml'
+    testfile_4.write_text(testcase_yaml_4)
+
     tmp_other_dir = tmp_test_root_dir / 'others'
     tmp_other_dir.mkdir()
     _ = tmp_other_dir / 'other.txt'
@@ -1402,6 +1439,7 @@ tests:
 
     env = mock.Mock(
         test_roots=[tmp_test_root_dir],
+        options=mock.Mock(detailed_test_id=detailed_id),
         alt_config_root=[tmp_alt_test_root_dir] if use_alt_root else []
     )
 
@@ -1410,6 +1448,7 @@ tests:
     res = testplan.add_testsuites(testsuite_filter)
 
     assert res == expected_suite_count
+    assert testplan.load_errors == expected_errors
 
 
 def test_testplan_str():