diff --git a/src/uu/pr/src/pr.rs b/src/uu/pr/src/pr.rs
index 843b3b8f970..58902cf17ef 100644
--- a/src/uu/pr/src/pr.rs
+++ b/src/uu/pr/src/pr.rs
@@ -276,14 +276,18 @@ pub fn uu_app() -> Command {
                 .short('s')
                 .long(options::COLUMN_CHAR_SEPARATOR)
                 .help(translate!("pr-help-column-char-separator"))
-                .value_name("char"),
+                .value_name("char")
+                .num_args(0..=1)
+                .default_missing_value("\t"),
         )
         .arg(
             Arg::new(options::COLUMN_STRING_SEPARATOR)
                 .short('S')
                 .long(options::COLUMN_STRING_SEPARATOR)
                 .help(translate!("pr-help-column-string-separator"))
-                .value_name("string"),
+                .value_name("string")
+                .num_args(0..=1)
+                .default_missing_value(" "),
         )
         .arg(
             Arg::new(options::MERGE)
diff --git a/tests/by-util/test_pr.rs b/tests/by-util/test_pr.rs
index 63063a7e732..d2e6cb675b7 100644
--- a/tests/by-util/test_pr.rs
+++ b/tests/by-util/test_pr.rs
@@ -627,3 +627,17 @@ fn test_page_header_width() {
     let regex = Regex::new(&pattern).unwrap();
     new_ucmd!().pipe_in("a").succeeds().stdout_matches(&regex);
 }
+
+#[test]
+fn test_separator_options_default_values() {
+    // -s and -S without arguments should use default values (TAB and space)
+    // TODO: verify output matches GNU pr behavior
+    new_ucmd!()
+        .args(&["-t", "-2", "-s"])
+        .pipe_in("a\nb\n")
+        .succeeds();
+    new_ucmd!()
+        .args(&["-t", "-2", "-S"])
+        .pipe_in("a\nb\n")
+        .succeeds();
+}