diff --git a/tests/coreutils.rs b/tests/coreutils.rs
index 6ebfeac..de16e8d 100644
--- a/tests/coreutils.rs
+++ b/tests/coreutils.rs
@@ -13,6 +13,9 @@ mod basename;
 #[path = "coreutils/cat.rs"]
 mod cat;
 
+#[path = "coreutils/cksum.rs"]
+mod cksum;
+
 #[path = "coreutils/dd.rs"]
 mod dd;
 
diff --git a/tests/coreutils/cksum.rs b/tests/coreutils/cksum.rs
new file mode 100644
index 0000000..71682fd
--- /dev/null
+++ b/tests/coreutils/cksum.rs
@@ -0,0 +1,201 @@
+use uutils_args::{Arguments, Options};
+
+#[derive(Debug, Clone, Arguments)]
+enum Arg {
+    #[arg("-b", "--binary")]
+    Binary,
+
+    #[arg("-t", "--text")]
+    Text,
+
+    #[arg("--tag")]
+    Tag,
+
+    #[arg("--untagged")]
+    Untagged,
+}
+
+#[derive(Default, Debug, PartialEq)]
+enum Tristate {
+    True,
+    #[default]
+    Unset,
+    False,
+}
+
+#[derive(Default, Debug)]
+struct Settings {
+    binary: Tristate,
+    tag: Tristate,
+}
+
+impl Options<Arg> for Settings {
+    fn apply(&mut self, arg: Arg) {
+        match arg {
+            Arg::Binary => self.binary = Tristate::True,
+            Arg::Text => self.binary = Tristate::False,
+            Arg::Tag => {
+                // https://github.com/uutils/coreutils/issues/6364
+                self.binary = Tristate::Unset;
+                self.tag = Tristate::True;
+            }
+            Arg::Untagged => {
+                // https://github.com/uutils/coreutils/issues/6364
+                if self.tag == Tristate::True {
+                    self.binary = Tristate::Unset;
+                }
+                self.tag = Tristate::False;
+            }
+        }
+    }
+}
+
+#[derive(Debug, PartialEq)]
+enum ResultingFormat {
+    UntaggedText,
+    UntaggedBinary,
+    Tagged,
+    ErrorInstead,
+}
+
+impl Settings {
+    fn format(&self) -> ResultingFormat {
+        // Interpret "Unset" as "tagged":
+        if self.tag != Tristate::False {
+            // -> Tagged.
+            // Error only if the user explicitly requests the text format:
+            if self.binary == Tristate::False {
+                ResultingFormat::ErrorInstead
+            } else {
+                ResultingFormat::Tagged
+            }
+        } else {
+            // -> Untagged.
+            // Binary only if the user explicitly requests it:
+            if self.binary == Tristate::True {
+                ResultingFormat::UntaggedBinary
+            } else {
+                ResultingFormat::UntaggedText
+            }
+        }
+    }
+}
+
+// Convenience function for testing
+#[cfg(test)]
+fn assert_format(args: &[&str], expected: ResultingFormat) {
+    let mut full_argv = vec!["bin_name"];
+    full_argv.extend(args);
+    let result = Settings::default().parse(full_argv).unwrap();
+    assert_eq!(
+        (result.0.format(), result.1.as_slice()),
+        (expected, [].as_slice()),
+        "{:?}",
+        args
+    );
+}
+
+// These tests basically force the reader to make the same conclusions as
+// https://github.com/uutils/coreutils/issues/6364
+// Quotes from the issue are marked with a leading ">".
+
+#[test]
+fn binary_text_toggle_in_tagged() {
+    // > Observe that -b/-t seems to be doing precisely what we would hope for: toggle between binary/text mode:
+    // -b/-t/--tagged switch between tagged/error behavior
+    assert_format(&[], ResultingFormat::Tagged);
+    assert_format(&["-t"], ResultingFormat::ErrorInstead);
+    assert_format(&["-t", "-b"], ResultingFormat::Tagged);
+    assert_format(&["-t", "--tag"], ResultingFormat::Tagged);
+}
+
+#[test]
+fn binary_text_toggle_in_untagged() {
+    // Once we're in untagged format, -b/-t switch between binary/text behavior
+    assert_format(&["--untagged"], ResultingFormat::UntaggedText);
+    assert_format(&["--untagged", "-t"], ResultingFormat::UntaggedText);
+    assert_format(&["--untagged", "-b"], ResultingFormat::UntaggedBinary);
+    assert_format(&["--untagged", "-t", "-b"], ResultingFormat::UntaggedBinary);
+    assert_format(&["--untagged", "-b", "-t"], ResultingFormat::UntaggedText);
+}
+
+// > Observe that --tag/--untagged seems to be the flags that have the weird behavior attached to
+// > them. In particular, the T state seems to be more that one actual state, probably
+// > differentiated along the "text-binary-axis".
+
+#[test]
+fn nondeterministic_edges() {
+    // Same behavior:
+    assert_format(&[], ResultingFormat::Tagged);
+    assert_format(&["-b"], ResultingFormat::Tagged);
+    // But must have different internal state:
+    assert_format(&["--untagged"], ResultingFormat::UntaggedText);
+    assert_format(&["-b", "--untagged"], ResultingFormat::UntaggedBinary);
+}
+
+#[test]
+fn selfloops() {
+    // "T"
+    assert_format(&[], ResultingFormat::Tagged);
+    assert_format(&["-b"], ResultingFormat::Tagged);
+    assert_format(&["--tag"], ResultingFormat::Tagged);
+    assert_format(&["-b", "--tag"], ResultingFormat::Tagged);
+    // "E"
+    assert_format(&["-t"], ResultingFormat::ErrorInstead);
+    assert_format(&["-t", "-t"], ResultingFormat::ErrorInstead);
+    // "A"
+    assert_format(&["-b", "--untagged"], ResultingFormat::UntaggedBinary);
+    assert_format(&["-b", "--untagged", "-b"], ResultingFormat::UntaggedBinary);
+    assert_format(
+        &["-b", "--untagged", "--untagged"],
+        ResultingFormat::UntaggedBinary,
+    );
+    // "S"
+    assert_format(&["--untagged"], ResultingFormat::UntaggedText);
+    assert_format(&["--untagged", "-t"], ResultingFormat::UntaggedText);
+    assert_format(&["--untagged", "--untagged"], ResultingFormat::UntaggedText);
+}
+
+#[test]
+fn other_diagonals() {
+    // From "A" and "S" ...
+    assert_format(&["-b", "--untagged"], ResultingFormat::UntaggedBinary);
+    assert_format(&["--untagged"], ResultingFormat::UntaggedText);
+    // ... to "T":
+    assert_format(&["-b", "--untagged", "--tag"], ResultingFormat::Tagged);
+    assert_format(&["--untagged", "--tag"], ResultingFormat::Tagged);
+    // From "E" to "S":
+    assert_format(&["-t"], ResultingFormat::ErrorInstead);
+    assert_format(&["-t", "--untagged"], ResultingFormat::UntaggedText);
+}
+
+#[test]
+fn suffix_b_u_not_deterministic() {
+    // > Ending in bU does not determine the result:
+    assert_format(&["-b", "--untagged"], ResultingFormat::UntaggedBinary);
+    assert_format(
+        &["--tag", "-b", "--untagged"],
+        ResultingFormat::UntaggedText,
+    );
+    assert_format(
+        &["--untagged", "-b", "--untagged"],
+        ResultingFormat::UntaggedBinary,
+    );
+    assert_format(
+        &["-b", "--untagged", "-b", "--untagged"],
+        ResultingFormat::UntaggedBinary,
+    );
+    assert_format(
+        &["--tag", "--untagged", "-b", "--untagged"],
+        ResultingFormat::UntaggedBinary,
+    );
+    assert_format(
+        &["--untagged", "--tag", "-b", "--untagged"],
+        ResultingFormat::UntaggedText,
+    );
+    // > Therefore, U does not set the binary-ness to a constant, but rather depends on the tagged-ness.
+}
+
+// I *think* that this battery of tests fully specifies the full behavior.
+// In any case, brute-forcing all of the 4^n combinations up to 5 arguments
+// shows no counter-examples, so this implementation is definitely a good match.