diff --git a/bindings/python/ns__init__.py b/bindings/python/ns__init__.py
index f0f3c5d20..6738d0d58 100644
--- a/bindings/python/ns__init__.py
+++ b/bindings/python/ns__init__.py
@@ -155,7 +155,7 @@ def extract_linked_libraries(library_name: str, prefix: str) -> tuple:
     linked_libs = []
     # First discover which 3rd-party libraries are used by the current module
     try:
-        with open(os.path.abspath(library_path), "rb") as f:
+        with open(os.path.abspath(library_path), "rb", encoding="utf-8") as f:
             linked_libs = re.findall(b"\x00(lib.*?.%b)" % LIBRARY_EXTENSION.encode("utf-8"), f.read())
     except Exception as e:
         print("Failed to extract libraries used by {library} with exception:{exception}"
diff --git a/doc/contributing/pickle-to-xml.py b/doc/contributing/pickle-to-xml.py
index 1f557370f..bf055d996 100755
--- a/doc/contributing/pickle-to-xml.py
+++ b/doc/contributing/pickle-to-xml.py
@@ -12,7 +12,7 @@ import os
 import codecs
 
 def dump_pickles(out, dirname, filename, path):
-    f = open(os.path.join(dirname, filename), 'r')
+    f = open(os.path.join(dirname, filename), 'r', encoding='utf-8')
     data = pickle.load(f)
     fragment_file = codecs.open(data['current_page_name'] + '.frag', mode='w', encoding='utf-8')
     fragment_file.write(data['body'])
diff --git a/doc/tutorial/pickle-to-xml.py b/doc/tutorial/pickle-to-xml.py
index 1f557370f..bf055d996 100755
--- a/doc/tutorial/pickle-to-xml.py
+++ b/doc/tutorial/pickle-to-xml.py
@@ -12,7 +12,7 @@ import os
 import codecs
 
 def dump_pickles(out, dirname, filename, path):
-    f = open(os.path.join(dirname, filename), 'r')
+    f = open(os.path.join(dirname, filename), 'r', encoding='utf-8')
     data = pickle.load(f)
     fragment_file = codecs.open(data['current_page_name'] + '.frag', mode='w', encoding='utf-8')
     fragment_file.write(data['body'])
diff --git a/src/flow-monitor/examples/flowmon-parse-results.py b/src/flow-monitor/examples/flowmon-parse-results.py
index bbc3c9f8b..eebc032fe 100644
--- a/src/flow-monitor/examples/flowmon-parse-results.py
+++ b/src/flow-monitor/examples/flowmon-parse-results.py
@@ -179,7 +179,7 @@ class Simulation(object):
 
 
 def main(argv):
-    file_obj = open(argv[1])
+    file_obj = open(argv[1], encoding="utf-8")
     print("Reading XML file ", end=" ")
 
     sys.stdout.flush()
diff --git a/src/spectrum/utils/two-ray-to-three-gpp-ch-calibration.py b/src/spectrum/utils/two-ray-to-three-gpp-ch-calibration.py
index a48f02c81..55c60d002 100644
--- a/src/spectrum/utils/two-ray-to-three-gpp-ch-calibration.py
+++ b/src/spectrum/utils/two-ray-to-three-gpp-ch-calibration.py
@@ -438,7 +438,7 @@ def print_cplusplus_map_from_fit_results(fit: pd.DataFrame, out_fname: str):
     out_str = out_str[0:-2]
     out_str += '}\n'
 
-    f = open(out_fname, "w")
+    f = open(out_fname, "w", encoding="utf-8")
     f.write(out_str)
     f.close()
 
@@ -499,7 +499,7 @@ if __name__ == '__main__':
             res = joblib.Parallel(n_jobs=10)(
                 joblib.delayed(fit_ftr_to_reference)(df, params_comb, num_search_grid_params, num_refinements) for params_comb in product(scenarios, is_los, frequencies))
 
-        f = open(fit_out_fname, "w")
+        f = open(fit_out_fname, "w", encoding="utf-8")
         f.write("scen\tcond\tfc\tsigma\tk\tdelta\tm\n")
         for line in res:
             f.write(line)
diff --git a/src/wifi/examples/reference/bianchi11ax.py b/src/wifi/examples/reference/bianchi11ax.py
index 43dbff0de..bd758f06b 100644
--- a/src/wifi/examples/reference/bianchi11ax.py
+++ b/src/wifi/examples/reference/bianchi11ax.py
@@ -129,7 +129,7 @@ ack_rates_160MHz = [6e6, 12e6, 12e6, 24e6, 24e6, 24e6, 24e6, 24e6, 24e6, 24e6, 2
 k = 1
 
 difs = 1
-fo = open("bianchi_11ax_difs.txt", "w")
+fo = open("bianchi_11ax_difs.txt", "w", encoding="utf-8")
 for i in range(len(data_rates_20MHz)):
     bianchi_result = bianchi_ax(data_rates_20MHz[i], ack_rates_20MHz[i], k, difs)
     str_s = str_result(bianchi_result, i, 20)
@@ -149,7 +149,7 @@ for i in range(len(data_rates_160MHz)):
 fo.close()
 
 difs = 0
-fo = open("bianchi_11ax_eifs.txt", "w")
+fo = open("bianchi_11ax_eifs.txt", "w", encoding="utf-8")
 for i in range(len(data_rates_20MHz)):
     bianchi_result = bianchi_ax(data_rates_20MHz[i], ack_rates_20MHz[i], k, difs)
     str_s = str_result(bianchi_result, i, 20)
diff --git a/test.py b/test.py
index 7ba7097df..793dd1b73 100755
--- a/test.py
+++ b/test.py
@@ -277,7 +277,7 @@ def translate_to_text(results_file, text_file):
     import xml.etree.ElementTree as ET
     et = ET.parse(results_file)
 
-    with open(text_file, 'w') as f:
+    with open(text_file, 'w', encoding='utf-8') as f:
         for test in et.findall('Test'):
             node_to_text(test, f)
 
@@ -303,7 +303,7 @@ def translate_to_html(results_file, html_file):
     html_file += '.html'
     print('Writing results to html file %s...' % html_file, end='')
 
-    with open(html_file, 'w') as f:
+    with open(html_file, 'w', encoding='utf-8') as f:
         f.write("<html>\n")
         f.write("<body>\n")
         f.write("<center><h1>ns-3 Test Results</h1></center>\n")
@@ -596,7 +596,7 @@ def read_ns3_config():
     f = None
     try:
         # sys.platform reports linux2 for python2 and linux for python3
-        f = open(lock_filename, "rt")
+        f = open(lock_filename, "rt", encoding="utf-8")
     except FileNotFoundError:
         print('The .lock-ns3 file was not found.  You must configure before running test.py.', file=sys.stderr)
         sys.exit(2)
@@ -616,7 +616,7 @@ def read_ns3_config():
     global NS3_BUILDDIR
     NS3_BUILDDIR = out_dir
 
-    with open(lock_filename) as f:
+    with open(lock_filename, encoding='utf-8') as f:
         for line in f.readlines():
             for item in interesting_config_items:
                 if line.startswith(item):
@@ -1296,7 +1296,7 @@ def run_tests():
     # do this since the tests will just append individual results to this file.
     #
     xml_results_file = os.path.join(testpy_output_dir, "results.xml")
-    with open(xml_results_file, 'w') as f:
+    with open(xml_results_file, 'w', encoding='utf-8') as f:
         f.write('<?xml version="1.0"?>\n')
         f.write('<Results>\n')
 
@@ -1768,7 +1768,7 @@ def run_tests():
             # XXX We could add some timing information to the examples, i.e. run
             # them through time and print the results here.
             #
-            with open(xml_results_file, 'a') as f:
+            with open(xml_results_file, 'a', encoding='utf-8') as f:
                 f.write('<Example>\n')
                 example_name = "  <Name>%s</Name>\n" % job.display_name
                 f.write(example_name)
@@ -1833,7 +1833,7 @@ def run_tests():
             # followed by a VALGR failing test suite of the same name.
             #
             if job.is_skip:
-                with open(xml_results_file, 'a') as f:
+                with open(xml_results_file, 'a', encoding='utf-8') as f:
                     f.write("<Test>\n")
                     f.write("  <Name>%s</Name>\n" % job.display_name)
                     f.write('  <Result>SKIP</Result>\n')
@@ -1841,10 +1841,10 @@ def run_tests():
                     f.write("</Test>\n")
             else:
                 if job.returncode == 0 or job.returncode == 1 or job.returncode == 2:
-                    with open(xml_results_file, 'a') as f_to, open(job.tmp_file_name) as f_from:
+                    with open(xml_results_file, 'a', encoding='utf-8') as f_to, open(job.tmp_file_name, encoding='utf-8') as f_from:
                         f_to.write(f_from.read())
                 else:
-                    with open(xml_results_file, 'a') as f:
+                    with open(xml_results_file, 'a', encoding='utf-8') as f:
                         f.write("<Test>\n")
                         f.write("  <Name>%s</Name>\n" % job.display_name)
                         f.write('  <Result>CRASH</Result>\n')
@@ -1864,7 +1864,7 @@ def run_tests():
     # individual pieces.  So, we need to finish off and close out the XML
     # document
     #
-    with open(xml_results_file, 'a') as f:
+    with open(xml_results_file, 'a', encoding='utf-8') as f:
         f.write('</Results>\n')
 
     #
diff --git a/utils.py b/utils.py
index 134bb234c..2be96c1d3 100644
--- a/utils.py
+++ b/utils.py
@@ -20,7 +20,7 @@ def get_list_from_file(file_path, list_name):
 
     # Read in the file if it exists.
     if os.path.exists(file_path):
-        with open(file_path, "r") as file_in:
+        with open(file_path, "r", encoding="utf-8") as file_in:
 
             # Look for the list.
             list_string = ""
@@ -58,7 +58,7 @@ def get_bool_from_file(file_path, bool_name, value_if_missing):
 
     # Read in the file if it exists.
     if os.path.exists(file_path):
-        with open(file_path, "r") as file_in:
+        with open(file_path, "r", encoding="utf-8") as file_in:
 
             # Look for the boolean variable.
             bool_found = False
diff --git a/utils/create-module.py b/utils/create-module.py
index a3881d4cd..8aff7f1be 100755
--- a/utils/create-module.py
+++ b/utils/create-module.py
@@ -336,7 +336,7 @@ def create_file(path, template, **kwargs):
     artifact_path = Path(path)
 
     #open file for (w)rite and in (t)ext mode
-    with artifact_path.open("wt") as f:
+    with artifact_path.open("wt", encoding="utf-8") as f:
         f.write(template.format(**kwargs))
 
 
diff --git a/utils/grid.py b/utils/grid.py
index 3303b69cc..e8293af8c 100644
--- a/utils/grid.py
+++ b/utils/grid.py
@@ -1608,7 +1608,7 @@ def read_data(filename):
     m3 = re.compile('event-int ([^ ]+) ([^ ]+) ([0-9]+) ([0-9]+)')
     m4 = re.compile('color ([^ ]+) #([a-fA-F0-9]{2,2})([a-fA-F0-9]{2,2})([a-fA-F0-9]{2,2})')
 
-    with open(filename) as fh:
+    with open(filename, encoding='utf-8') as fh:
         for line in fh.readlines():
             m = m1.match(line)
             if m:
diff --git a/utils/tests/TestBase.py b/utils/tests/TestBase.py
index 58cfa4877..b23aaddbc 100644
--- a/utils/tests/TestBase.py
+++ b/utils/tests/TestBase.py
@@ -121,9 +121,9 @@ class TestBaseClass:
         passed = 0
         progress = 0.0
         failed_cases = []
-        with open(self.options.out_file, 'w') as out:
+        with open(self.options.out_file, 'w', encoding='utf-8') as out:
             outstream = out
-            with open(os.devnull, 'w') as sink:
+            with open(os.devnull, 'w', encoding='utf-8') as sink:
                 if self.options.mute:
                     outstream = sink
                 for cmd in cmds:
diff --git a/utils/tests/test-ns3.py b/utils/tests/test-ns3.py
index 34c55528d..27880a240 100755
--- a/utils/tests/test-ns3.py
+++ b/utils/tests/test-ns3.py
@@ -126,7 +126,7 @@ def get_programs_list():
     @return list of programs.
     """
     values = {}
-    with open(ns3_lock_filename) as f:
+    with open(ns3_lock_filename, encoding="utf-8") as f:
         exec(f.read(), globals(), values)
 
     programs_list = values["ns3_runnable_programs"]
@@ -163,7 +163,7 @@ def read_lock_entry(entry):
     @return value of the requested entry.
     """
     values = {}
-    with open(ns3_lock_filename) as f:
+    with open(ns3_lock_filename, encoding="utf-8") as f:
         exec(f.read(), globals(), values)
     return values.get(entry, None)
 
@@ -206,7 +206,7 @@ class DockerContainerManager:
             currentTestCase.skipTest("python-on-whales was not found")
 
         # Import rootless docker settings from .bashrc
-        with open(os.path.expanduser("~/.bashrc"), "r") as f:
+        with open(os.path.expanduser("~/.bashrc"), "r", encoding="utf-8") as f:
             docker_settings = re.findall("(DOCKER_.*=.*)", f.read())
             for setting in docker_settings:
                 key, value = setting.split("=")
@@ -285,7 +285,7 @@ class NS3UnusedSourcesTestCase(unittest.TestCase):
                 continue
 
             # Open the examples CMakeLists.txt and read it
-            with open(os.path.join(example_directory, "CMakeLists.txt"), "r") as f:
+            with open(os.path.join(example_directory, "CMakeLists.txt"), "r", encoding="utf-8") as f:
                 cmake_contents = f.read()
 
             # For each file, check if it is in the CMake contents
@@ -319,7 +319,7 @@ class NS3UnusedSourcesTestCase(unittest.TestCase):
                 cmake_path = os.path.join(parent_directory, os.path.basename(cmake_path))
 
             # Open the module CMakeLists.txt and read it
-            with open(cmake_path, "r") as f:
+            with open(cmake_path, "r", encoding="utf-8") as f:
                 cmake_contents = f.read()
 
             # For each file, check if it is in the CMake contents
@@ -358,7 +358,7 @@ class NS3UnusedSourcesTestCase(unittest.TestCase):
                 cmake_path = os.path.join(parent_directory, os.path.basename(cmake_path))
 
             # Open the module CMakeLists.txt and read it
-            with open(cmake_path, "r") as f:
+            with open(cmake_path, "r", encoding="utf-8") as f:
                 cmake_contents = f.read()
 
             # For each file, check if it is in the CMake contents
@@ -389,7 +389,7 @@ class NS3DependenciesTestCase(unittest.TestCase):
         for path in module_paths:
             # Open the module CMakeLists.txt and read it
             cmake_path = os.path.join(path, "CMakeLists.txt")
-            with open(cmake_path, "r") as f:
+            with open(cmake_path, "r", encoding="utf-8") as f:
                 cmake_contents = f.readlines()
 
             module_name = os.path.relpath(path, ns3_path)
@@ -957,7 +957,7 @@ class NS3ConfigureTestCase(NS3BaseTestCase):
             ns3rc_template = ns3rc_str(ns3rc_type)
 
             # Now we repeat the command line tests but with the ns3rc file.
-            with open(ns3rc_script, "w") as f:
+            with open(ns3rc_script, "w", encoding="utf-8") as f:
                 f.write(ns3rc_template.format(modules="'lte'", examples="False", tests="True"))
 
             # Reconfigure.
@@ -972,7 +972,7 @@ class NS3ConfigureTestCase(NS3BaseTestCase):
             self.assertLessEqual(len(get_programs_list()), len(self.ns3_executables))
 
             # Replace the ns3rc file with the wifi module, enabling examples and disabling tests
-            with open(ns3rc_script, "w") as f:
+            with open(ns3rc_script, "w", encoding="utf-8") as f:
                 f.write(ns3rc_template.format(modules="'wifi'", examples="True", tests="False"))
 
             # Reconfigure
@@ -987,7 +987,7 @@ class NS3ConfigureTestCase(NS3BaseTestCase):
             self.assertGreater(len(get_programs_list()), len(self.ns3_executables))
 
             # Replace the ns3rc file with multiple modules
-            with open(ns3rc_script, "w") as f:
+            with open(ns3rc_script, "w", encoding="utf-8") as f:
                 f.write(ns3rc_template.format(modules="'core','network'", examples="True", tests="False"))
 
             # Reconfigure
@@ -1004,7 +1004,7 @@ class NS3ConfigureTestCase(NS3BaseTestCase):
 
             # Replace the ns3rc file with multiple modules,
             # in various different ways and with comments
-            with open(ns3rc_script, "w") as f:
+            with open(ns3rc_script, "w", encoding="utf-8") as f:
                 if ns3rc_type == "python":
                     f.write(ns3rc_template.format(modules="""'core', #comment
                     'lte',
@@ -1126,7 +1126,7 @@ class NS3ConfigureTestCase(NS3BaseTestCase):
 
         # Cause a sigsegv
         sigsegv_example = os.path.join(ns3_path, "scratch", "sigsegv.cc")
-        with open(sigsegv_example, "w") as f:
+        with open(sigsegv_example, "w", encoding="utf-8") as f:
             f.write("""
                     int main (int argc, char *argv[])
                     {
@@ -1144,7 +1144,7 @@ class NS3ConfigureTestCase(NS3BaseTestCase):
 
         # Cause an abort
         abort_example = os.path.join(ns3_path, "scratch", "abort.cc")
-        with open(abort_example, "w") as f:
+        with open(abort_example, "w", encoding="utf-8") as f:
             f.write("""
                     #include "ns3/core-module.h"
 
@@ -1217,7 +1217,7 @@ class NS3ConfigureTestCase(NS3BaseTestCase):
         for path in test_files + backup_files:
             filepath = os.path.join(ns3_path, path)
             os.makedirs(os.path.dirname(filepath), exist_ok=True)
-            with open(filepath, "w") as f:
+            with open(filepath, "w", encoding="utf-8") as f:
                 if "main" in path:
                     f.write("int main (int argc, char *argv[]){}")
                 else:
@@ -1358,10 +1358,10 @@ class NS3ConfigureTestCase(NS3BaseTestCase):
         os.makedirs("contrib/borked/examples", exist_ok=True)
 
         # Test if configuration succeeds and building the module library fails
-        with open("contrib/borked/examples/CMakeLists.txt", "w") as f:
+        with open("contrib/borked/examples/CMakeLists.txt", "w", encoding="utf-8") as f:
             f.write("")
         for invalid_or_nonexistent_library in ["", "gsd", "lib", "libfi", "calibre"]:
-            with open("contrib/borked/CMakeLists.txt", "w") as f:
+            with open("contrib/borked/CMakeLists.txt", "w", encoding="utf-8") as f:
                 f.write("""
                         build_lib(
                             LIBNAME borked
@@ -1400,7 +1400,7 @@ class NS3ConfigureTestCase(NS3BaseTestCase):
         # - no additional library (should work)
         # - invalid library names (should fail to configure)
         # - valid library names but nonexistent libraries (should not create a target)
-        with open("contrib/borked/CMakeLists.txt", "w") as f:
+        with open("contrib/borked/CMakeLists.txt", "w", encoding="utf-8") as f:
             f.write("""
                     build_lib(
                         LIBNAME borked
@@ -1409,7 +1409,7 @@ class NS3ConfigureTestCase(NS3BaseTestCase):
                     )
                     """)
         for invalid_or_nonexistent_library in ["", "gsd", "lib", "libfi", "calibre"]:
-            with open("contrib/borked/examples/CMakeLists.txt", "w") as f:
+            with open("contrib/borked/examples/CMakeLists.txt", "w", encoding="utf-8") as f:
                 f.write("""
                         build_lib_example(
                             NAME borked-example
@@ -1452,9 +1452,9 @@ class NS3ConfigureTestCase(NS3BaseTestCase):
         os.makedirs("contrib/calibre/examples", exist_ok=True)
 
         # Now test if we can have a library with "lib" in it
-        with open("contrib/calibre/examples/CMakeLists.txt", "w") as f:
+        with open("contrib/calibre/examples/CMakeLists.txt", "w", encoding="utf-8") as f:
             f.write("")
-        with open("contrib/calibre/CMakeLists.txt", "w") as f:
+        with open("contrib/calibre/CMakeLists.txt", "w", encoding="utf-8") as f:
             f.write("""
                 build_lib(
                     LIBNAME calibre
@@ -1539,7 +1539,7 @@ class NS3ConfigureTestCase(NS3BaseTestCase):
                                       "VERSION_TAG_DISTANCE = '0'\n"
                                       "VERSION_BUILD_PROFILE = 'debug'\n"
                                       )
-            with open(version_cache_file, "w") as version:
+            with open(version_cache_file, "w", encoding="utf-8") as version:
                 version.write(version_cache_contents)
 
             # Configuration should now succeed
@@ -1549,7 +1549,7 @@ class NS3ConfigureTestCase(NS3BaseTestCase):
             self.assertTrue(os.path.exists(os.path.join(ns3_path, "cmake-cache", "build.ninja")))
 
             # And contents of version cache should be unchanged
-            with open(version_cache_file, "r") as version:
+            with open(version_cache_file, "r", encoding="utf-8") as version:
                 self.assertEqual(version.read(), version_cache_contents)
 
             # Third case: we rename the .git directory temporarily and reconfigure
@@ -1571,7 +1571,7 @@ class NS3ConfigureTestCase(NS3BaseTestCase):
             container.execute("./ns3 configure -G Ninja --enable-build-version")
             container.execute("./ns3 build core")
             self.assertTrue(os.path.exists(os.path.join(ns3_path, "cmake-cache", "build.ninja")))
-            with open(version_cache_file, "r") as version:
+            with open(version_cache_file, "r", encoding="utf-8") as version:
                 self.assertNotEqual(version.read(), version_cache_contents)
 
             # Remove version cache file if it exists
@@ -1638,7 +1638,7 @@ class NS3ConfigureTestCase(NS3BaseTestCase):
 
             # Check if configuration properly detected lld
             self.assertTrue(os.path.exists(os.path.join(ns3_path, "cmake-cache", "build.ninja")))
-            with open(os.path.join(ns3_path, "cmake-cache", "build.ninja"), "r") as f:
+            with open(os.path.join(ns3_path, "cmake-cache", "build.ninja"), "r", encoding="utf-8") as f:
                 self.assertIn("-fuse-ld=lld", f.read())
 
             # Try to build using the lld linker
@@ -1659,7 +1659,7 @@ class NS3ConfigureTestCase(NS3BaseTestCase):
 
             # Check if configuration properly detected mold
             self.assertTrue(os.path.exists(os.path.join(ns3_path, "cmake-cache", "build.ninja")))
-            with open(os.path.join(ns3_path, "cmake-cache", "build.ninja"), "r") as f:
+            with open(os.path.join(ns3_path, "cmake-cache", "build.ninja"), "r", encoding="utf-8") as f:
                 self.assertIn("-fuse-ld=mold", f.read())
 
             # Try to build using the lld linker
@@ -1676,7 +1676,7 @@ class NS3ConfigureTestCase(NS3BaseTestCase):
 
             # Check if configuration properly disabled lld/mold usage
             self.assertTrue(os.path.exists(os.path.join(ns3_path, "cmake-cache", "build.ninja")))
-            with open(os.path.join(ns3_path, "cmake-cache", "build.ninja"), "r") as f:
+            with open(os.path.join(ns3_path, "cmake-cache", "build.ninja"), "r", encoding="utf-8") as f:
                 self.assertNotIn("-fuse-ld=mold", f.read())
 
     def test_21_ClangTimeTrace(self):
@@ -1958,7 +1958,7 @@ class NS3BuildBaseTestCase(NS3BaseTestCase):
         self.ns3_libraries = get_libraries_list()
 
         version_file = os.sep.join([ns3_path, "VERSION"])
-        with open(version_file, "w") as f:
+        with open(version_file, "w", encoding="utf-8") as f:
             f.write("3-00\n")
 
         # Reconfigure.
@@ -1990,7 +1990,7 @@ class NS3BuildBaseTestCase(NS3BaseTestCase):
             self.assertTrue(os.path.exists(library))
 
         # Restore version file.
-        with open(version_file, "w") as f:
+        with open(version_file, "w", encoding="utf-8") as f:
             f.write("3-dev\n")
 
     def test_07_OutputDirectory(self):
@@ -2077,7 +2077,7 @@ class NS3BuildBaseTestCase(NS3BaseTestCase):
 
         # 3-dev version format is not supported by CMake, so we use 3.01.
         version_file = os.sep.join([ns3_path, "VERSION"])
-        with open(version_file, "w") as f:
+        with open(version_file, "w", encoding="utf-8") as f:
             f.write("3-01\n")
 
         # Reconfigure setting the installation folder to ns-3-dev/build/install.
@@ -2113,7 +2113,7 @@ class NS3BuildBaseTestCase(NS3BaseTestCase):
 
         # Now create a test CMake project and try to find_package ns-3.
         test_main_file = os.sep.join([install_prefix, "main.cpp"])
-        with open(test_main_file, "w") as f:
+        with open(test_main_file, "w", encoding="utf-8") as f:
             f.write("""
             #include <ns3/core-module.h>
             using namespace ns3;
@@ -2163,7 +2163,7 @@ class NS3BuildBaseTestCase(NS3BaseTestCase):
                                      """ + import_method
 
                 test_cmake_project_file = os.sep.join([install_prefix, "CMakeLists.txt"])
-                with open(test_cmake_project_file, "w") as f:
+                with open(test_cmake_project_file, "w", encoding="utf-8") as f:
                     f.write(test_cmake_project)
 
                 # Configure the test project
@@ -2215,7 +2215,7 @@ class NS3BuildBaseTestCase(NS3BaseTestCase):
 
         # Restore 3-dev version file
         os.remove(version_file)
-        with open(version_file, "w") as f:
+        with open(version_file, "w", encoding="utf-8") as f:
             f.write("3-dev\n")
 
     def test_09_Scratches(self):
@@ -2999,7 +2999,7 @@ class NS3QualityControlTestCase(unittest.TestCase):
                         continue
 
                     try:
-                        with open(filepath, "r") as f:
+                        with open(filepath, "r", encoding="utf-8") as f:
                             matches = regex.findall(f.read())
 
                             # Get first group for each match (containing the URL)