diff --git a/NEWS.md b/NEWS.md
index 323f5bb..0a82989 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,6 +1,7 @@
 27.0 (Not released yet)
 =======================
 
+* `e3.testsuite.optfileparser`: restrict syntax for discriminants.
 * Fix test filtering when not all test finders have dedicated directories.
 * `PatternSubstitute`: update annotations to accept replacement callbacks.
 * `e3.testsuite.report.xunit`: add a `XUnitImportApp` class to make it possible
diff --git a/src/e3/testsuite/optfileparser.py b/src/e3/testsuite/optfileparser.py
index dedad0f..2c14972 100644
--- a/src/e3/testsuite/optfileparser.py
+++ b/src/e3/testsuite/optfileparser.py
@@ -22,7 +22,17 @@
 
 
 # Regexp that matches valid lines in test.opt files
-OPTLINE_REGEXPS = re.compile(r"^([^\s]+)(\s+([a-zA-Z0-9_-]+)(\s+(.*))?)?$")
+OPTLINE_REGEXPS = re.compile(
+    # Comma-separated list of discriminants
+    r"^([a-zA-Z0-9!+,._-]+)"
+    # The rest is optional...
+    "("
+    # Command
+    r"\s+([a-zA-Z0-9_-]+)"
+    # Optional command argument
+    r"(\s+(.*))?"
+    ")?$"
+)
 
 
 class BadFormattingError(Exception):
diff --git a/tests/tests/optfiles/sharp_in_comment.opt b/tests/tests/optfiles/sharp_in_comment.opt
new file mode 100644
index 0000000..9ae4dad
--- /dev/null
+++ b/tests/tests/optfiles/sharp_in_comment.opt
@@ -0,0 +1 @@
+ALL DEAD # This # can # contain # sharps
diff --git a/tests/tests/optfiles/syntax_error_3.opt b/tests/tests/optfiles/syntax_error_3.opt
new file mode 100644
index 0000000..6e51e91
--- /dev/null
+++ b/tests/tests/optfiles/syntax_error_3.opt
@@ -0,0 +1 @@
+# This is not a comment and should be rejected
diff --git a/tests/tests/test_optfileparser.py b/tests/tests/test_optfileparser.py
index a9b626b..efa168b 100644
--- a/tests/tests/test_optfileparser.py
+++ b/tests/tests/test_optfileparser.py
@@ -220,3 +220,19 @@ def test_check_syntax_main():
     p = Run(["e3-opt-check", "dead.opt", "tags.opt"], cwd=optfiles_dir)
     assert p.status == 0
     assert p.out == ""
+
+
+def test_sharp():
+    """Check the handling for lines that contain '#'."""
+    of = parse_file("sharp_in_comment.opt")
+    assert of.get_value("dead") == "# This # can # contain # sharps"
+
+    try:
+        parse_file("syntax_error_3.opt")
+    except BadFormattingError as exc:
+        assert str(exc) == (
+            "Can not parse line 1:"
+            " # This is not a comment and should be rejected"
+        )
+    else:
+        raise AssertionError()