diff --git a/src/uu/du/src/du.rs b/src/uu/du/src/du.rs
index fa91da7ac24..e748d4d7fc6 100644
--- a/src/uu/du/src/du.rs
+++ b/src/uu/du/src/du.rs
@@ -1233,9 +1233,12 @@ fn parse_time_style(s: Option<&String>) -> UResult<String> {
                 // the string starts with +, and ignore "locale".
                 Ok(s) => {
                     let s = s.strip_prefix("posix-").unwrap_or(s.as_str());
-                    let s = match s.chars().next().unwrap() {
-                        '+' => s.split('\n').next().unwrap(),
-                        _ => s,
+                    // `s` can be empty here (e.g. TIME_STYLE=posix-), so test the
+                    // prefix instead of unwrapping the first char.
+                    let s = if s.starts_with('+') {
+                        s.split('\n').next().unwrap()
+                    } else {
+                        s
                     };
                     match s {
                         "locale" => None,
@@ -1251,9 +1254,9 @@ fn parse_time_style(s: Option<&String>) -> UResult<String> {
             "full-iso" => Ok(format::FULL_ISO.to_string()),
             "long-iso" => Ok(format::LONG_ISO.to_string()),
             "iso" => Ok(format::ISO.to_string()),
-            _ => match s.chars().next().unwrap() {
-                '+' => Ok(s[1..].to_string()),
-                _ => Err(DuError::InvalidTimeStyleArg(s).into()),
+            _ => match s.strip_prefix('+') {
+                Some(rest) => Ok(rest.to_string()),
+                None => Err(DuError::InvalidTimeStyleArg(s).into()),
             },
         },
         None => Ok(format::LONG_ISO.to_string()),
diff --git a/src/uu/ls/src/config.rs b/src/uu/ls/src/config.rs
index 3a879b83735..fc788e85425 100644
--- a/src/uu/ls/src/config.rs
+++ b/src/uu/ls/src/config.rs
@@ -1054,19 +1054,19 @@ fn parse_time_style(options: &clap::ArgMatches) -> Result<(String, Option<String
                     Some(format::ISO.to_string() + " "),
                 )),
                 "locale" => ok(LOCALE_FORMAT),
-                _ => match field.chars().next().unwrap() {
-                    '+' => {
-                        // recent/older formats are (optionally) separated by a newline
-                        let mut it = field[1..].split('\n');
-                        let recent = it.next().unwrap_or_default();
-                        let older = it.next();
-                        match it.next() {
-                            None => ok((recent, older)),
-                            Some(_) => Err(LsError::TimeStyleParseError(String::from(field))),
-                        }
+                // `field` can be empty here (e.g. --time-style=posix-), so test
+                // the prefix instead of unwrapping the first char.
+                _ if field.starts_with('+') => {
+                    // recent/older formats are (optionally) separated by a newline
+                    let mut it = field[1..].split('\n');
+                    let recent = it.next().unwrap_or_default();
+                    let older = it.next();
+                    match it.next() {
+                        None => ok((recent, older)),
+                        Some(_) => Err(LsError::TimeStyleParseError(String::from(field))),
                     }
-                    _ => Err(LsError::TimeStyleParseError(String::from(field))),
-                },
+                }
+                _ => Err(LsError::TimeStyleParseError(String::from(field))),
             }
         }
     } else if options.get_flag(options::FULL_TIME) {
diff --git a/tests/by-util/test_du.rs b/tests/by-util/test_du.rs
index 7dfda01fd4a..30e8ab111e7 100644
--- a/tests/by-util/test_du.rs
+++ b/tests/by-util/test_du.rs
@@ -188,6 +188,21 @@ fn test_du_with_posixly_correct() {
     assert_eq!(expected, result);
 }
 
+#[test]
+fn test_du_time_style_empty() {
+    let ts = TestScenario::new(util_name!());
+    ts.fixtures.mkdir("a");
+    ts.ucmd()
+        .args(&["--time", "--time-style=", "a"])
+        .fails_with_code(1)
+        .stderr_contains("du: invalid argument '' for 'time style'");
+    ts.ucmd()
+        .args(&["--time", "a"])
+        .env("TIME_STYLE", "posix-")
+        .fails_with_code(1)
+        .stderr_contains("du: invalid argument '' for 'time style'");
+}
+
 #[test]
 fn test_du_zero_env_block_size() {
     let ts = TestScenario::new(util_name!());
diff --git a/tests/by-util/test_ls.rs b/tests/by-util/test_ls.rs
index 55e9b22e112..8965aaadc7c 100644
--- a/tests/by-util/test_ls.rs
+++ b/tests/by-util/test_ls.rs
@@ -167,6 +167,15 @@ fn test_invalid_value_time_style() {
         .no_stderr();
 }
 
+#[test]
+fn test_time_style_empty_after_posix_prefix() {
+    new_ucmd!()
+        .arg("-l")
+        .arg("--time-style=posix-")
+        .fails_with_code(2)
+        .stderr_contains("ls: invalid --time-style argument ''");
+}
+
 #[test]
 fn test_ls_ls() {
     new_ucmd!().succeeds();