diff --git a/DEVELOPMENT.md b/DEVELOPMENT.md
index 4f885e085dd..35291369c12 100644
--- a/DEVELOPMENT.md
+++ b/DEVELOPMENT.md
@@ -262,6 +262,7 @@ To generate [gcov-based](https://github.com/mozilla/grcov#example-how-to-generat
 export CARGO_INCREMENTAL=0
 export RUSTFLAGS="-Cinstrument-coverage -Ccodegen-units=1 -Copt-level=0 -Clink-dead-code -Coverflow-checks=off -Zpanic_abort_tests -Cpanic=abort"
 export RUSTDOCFLAGS="-Cpanic=abort"
+export RUSTUP_TOOLCHAIN="nightly"
 cargo build <options...> # e.g., --features feat_os_unix
 cargo test <options...> # e.g., --features feat_os_unix test_pathchk
 grcov . -s . --binary-path ./target/debug/ -t html --branch --ignore-not-existing --ignore build.rs --excl-br-line "^\s*((debug_)?assert(_eq|_ne)?\#\[derive\()" -o ./target/debug/coverage/
diff --git a/src/uu/timeout/src/timeout.rs b/src/uu/timeout/src/timeout.rs
index 3e1a35c45b2..290b5051f29 100644
--- a/src/uu/timeout/src/timeout.rs
+++ b/src/uu/timeout/src/timeout.rs
@@ -263,7 +263,14 @@ fn wait_or_kill_process(
     match process.wait_or_timeout(duration, None) {
         Ok(Some(status)) => {
             if preserve_status {
-                Ok(status.code().unwrap_or_else(|| status.signal().unwrap()))
+                let exit_code = status.code().unwrap_or_else(|| {
+                    status.signal().unwrap_or_else(|| {
+                        // Extremely rare: process exited but we have neither exit code nor signal.
+                        // This can happen on some platforms or in unusual termination scenarios.
+                        ExitStatus::TimeoutFailed.into()
+                    })
+                });
+                Ok(exit_code)
             } else {
                 Ok(ExitStatus::TimeoutFailed.into())
             }
@@ -351,10 +358,14 @@ fn timeout(
     // structure of `wait_or_kill_process()`. They can probably be
     // refactored into some common function.
     match process.wait_or_timeout(duration, Some(&SIGNALED)) {
-        Ok(Some(status)) => Err(status
-            .code()
-            .unwrap_or_else(|| preserve_signal_info(status.signal().unwrap()))
-            .into()),
+        Ok(Some(status)) => {
+            let exit_code = status.code().unwrap_or_else(|| {
+                status
+                    .signal()
+                    .map_or_else(|| ExitStatus::TimeoutFailed.into(), preserve_signal_info)
+            });
+            Err(exit_code.into())
+        }
         Ok(None) => {
             report_if_verbose(signal, &cmd[0], verbose);
             send_signal(process, signal, foreground);