diff --git a/docs/news.d/1240.bugfix.rst b/docs/news.d/1240.bugfix.rst
new file mode 100644
index 000000000..112e034db
--- /dev/null
+++ b/docs/news.d/1240.bugfix.rst
@@ -0,0 +1,3 @@
+Fixed a ``KeyError`` during test prioritization on subsequent runs when
+``scan_tests_from_file()`` was given a relative path, a ``pathlib.Path``, or a
+forward-slash path on Windows instead of the project's exact source filename.
diff --git a/tests/unit/test_test_scheduler.py b/tests/unit/test_test_scheduler.py
index 13659d72c..ca49f8eba 100644
--- a/tests/unit/test_test_scheduler.py
+++ b/tests/unit/test_test_scheduler.py
@@ -9,6 +9,7 @@
 """
 
 import unittest
+from pathlib import Path
 from unittest import mock
 from vunit.test.runner import TestScheduler
 
@@ -63,6 +64,16 @@ def test_that_new_test_suites_go_to_set_2(self):
                 self.assertEqual(result[set_idx]["total_exec_time"], 0)
                 self.assertEqual(len(result[set_idx]["test_suites"]), 0)
 
+    def test_that_scanned_file_with_different_path_spelling_and_history_goes_to_set_3(self):
+        test_suite = self._create_test_suite("lib1.tb1.test1", ["lib1.tb1.test1"], "tests.vhd")
+        self._add_test_history(test_suite.name, test_suite.name, "passed", 1, 10)
+        latest_dependency_updates = {str(Path("tests.vhd").resolve()): 0}
+
+        scheduler = TestScheduler([test_suite], 1, latest_dependency_updates, self._test_history)
+        result = scheduler._create_test_suite_sets([test_suite])
+
+        self.assertEqual(result[3]["test_suites"], [{"test_suite": test_suite, "exec_time": 10}])
+
     def test_that_skipped_test_suites_go_to_set_2(self):
         latest_dependency_updates = dict(file1=0)
         test_suites = [self._create_test_suite("lib1.tb1.test1", ["lib1.tb1.test1"], "file1")]
diff --git a/vunit/test/runner.py b/vunit/test/runner.py
index 0cc986159..4d909e554 100644
--- a/vunit/test/runner.py
+++ b/vunit/test/runner.py
@@ -458,9 +458,12 @@ def _create_test_suite_sets(self, test_suites):
                     if test_data:
                         if test_data["total_time"] is not None:
                             exec_time += test_data["total_time"]
-                        updated_dependency = self._latest_dependency_updates[test_suite.file_name] > test_data.get(
-                            "start_time", 0
-                        )
+                        # Tests may be scanned from a file which is not a project source file
+                        # (scan_tests_from_file). Without dependency information, treat it as
+                        # updated like _get_latest_dependency_updates does for changed files.
+                        updated_dependency = self._latest_dependency_updates.get(
+                            test_suite.file_name, 10e9
+                        ) > test_data.get("start_time", 0)
 
                         if test_data["skipped"]:
                             set_idx = 2
diff --git a/vunit/ui/__init__.py b/vunit/ui/__init__.py
index 17503a6c8..52b75baf8 100644
--- a/vunit/ui/__init__.py
+++ b/vunit/ui/__init__.py
@@ -1032,7 +1032,8 @@ def _get_test_list_depending_on_change(self, test_list):
             self._test_history = self._get_test_history(simulator_if=None)
 
         def depending_on_change(test_suite):
-            latest_dependency_update = self._latest_dependency_updates[test_suite.file_name]
+            # Unknown files (tests scanned from a non-project file) count as changed
+            latest_dependency_update = self._latest_dependency_updates.get(test_suite.file_name, 10e9)
             test_suite_history = self._test_history.get(test_suite.name, None)
             if test_suite_history:
                 test_start_times = [test_data["start_time"] for test_data in test_suite_history.values()]
diff --git a/vunit/ui/testbench.py b/vunit/ui/testbench.py
index db9a0a788..342c54d7e 100644
--- a/vunit/ui/testbench.py
+++ b/vunit/ui/testbench.py
@@ -9,6 +9,7 @@
 """
 
 from fnmatch import fnmatch
+from pathlib import Path
 from .common import lower_generics
 from .test import Test
 
@@ -240,4 +241,21 @@ def scan_tests_from_file(self, file_name):
            the ``NESTED_TEST_SUITE`` macro should be used instead of
            the ``TEST_SUITE`` macro.
         """
-        self._test_bench.scan_tests_from_file(file_name)
+        self._test_bench.scan_tests_from_file(self._get_project_file_name(file_name))
+
+    def _get_project_file_name(self, file_name):
+        """
+        Return the name under which the project knows file_name.
+
+        Test suites are associated with the file their tests are scanned from, and that
+        name is used to look up dependency information (e.g. for test prioritization).
+        The project knows a source file by its resolved path, or by the path of its
+        preprocessed copy if preprocessing is enabled. Map any spelling of the path
+        (relative, pathlib.Path, posix style on Windows, original instead of preprocessed
+        file) to that name. Files which are not part of the project are returned resolved.
+        """
+        path = Path(file_name).resolve()
+        for source_file in self._library._project.get_source_files_in_order():  # pylint: disable=protected-access
+            if Path(source_file.original_name).resolve() == path:
+                return source_file.name
+        return str(path)