diff --git a/changelog/7781.bugfix.rst b/changelog/7781.bugfix.rst
new file mode 100644
index 00000000000..191fcd4daf4
--- /dev/null
+++ b/changelog/7781.bugfix.rst
@@ -0,0 +1 @@
+Fix writing non-encodable text to log file when using ``--debug``.
diff --git a/src/_pytest/helpconfig.py b/src/_pytest/helpconfig.py
index 6b6718a7083..430870608bd 100644
--- a/src/_pytest/helpconfig.py
+++ b/src/_pytest/helpconfig.py
@@ -105,7 +105,7 @@ def pytest_cmdline_parse():
     if config.option.debug:
         # --debug | --debug <file.log> was provided.
         path = config.option.debug
-        debugfile = open(path, "w")
+        debugfile = open(path, "w", encoding="utf-8")
         debugfile.write(
             "versions pytest-%s, "
             "python-%s\ncwd=%s\nargs=%s\n\n"