diff --git a/src/header/stdio/default.rs b/src/header/stdio/default.rs
index 02a3708dd3..2e3aaa14c2 100644
--- a/src/header/stdio/default.rs
+++ b/src/header/stdio/default.rs
@@ -3,6 +3,7 @@ use core::{cell::UnsafeCell, ptr};
 
 use crate::{
     fs::File,
+    header::pthread,
     io::LineWriter,
     platform::types::*,
     sync::{Mutex, Once},
@@ -16,8 +17,12 @@ impl GlobalFile {
     fn new(file: c_int, flags: c_int) -> Self {
         let file = File::new(file);
         let writer = Box::new(LineWriter::new(unsafe { file.get_ref() }));
+        let mut mutex_attr = pthread::RlctMutexAttr {
+            ty: pthread::PTHREAD_MUTEX_RECURSIVE,
+            ..Default::default()
+        };
         GlobalFile(UnsafeCell::new(FILE {
-            lock: Mutex::new(()),
+            lock: pthread::RlctMutex::new(&mutex_attr).unwrap(),
 
             file,
             flags: constants::F_PERM | flags,
diff --git a/src/header/stdio/helpers.rs b/src/header/stdio/helpers.rs
index e2822ec4c4..0abc310121 100644
--- a/src/header/stdio/helpers.rs
+++ b/src/header/stdio/helpers.rs
@@ -8,6 +8,7 @@ use crate::{
     header::{
         errno::{self, EINVAL},
         fcntl::*,
+        pthread,
     },
     io::BufWriter,
     platform::{self, types::*},
@@ -69,9 +70,12 @@ pub fn _fdopen(fd: c_int, mode: CStr) -> Result<Box<FILE>, Errno> {
 
     let file = File::new(fd);
     let writer = Box::new(BufWriter::new(unsafe { file.get_ref() }));
-
+    let mut mutex_attr = pthread::RlctMutexAttr {
+        ty: pthread::PTHREAD_MUTEX_RECURSIVE,
+        ..Default::default()
+    };
     Ok(Box::new(FILE {
-        lock: Mutex::new(()),
+        lock: pthread::RlctMutex::new(&mutex_attr).unwrap(),
 
         file,
         flags,
diff --git a/src/header/stdio/mod.rs b/src/header/stdio/mod.rs
index 8470c59887..ac99bbfebd 100644
--- a/src/header/stdio/mod.rs
+++ b/src/header/stdio/mod.rs
@@ -23,7 +23,9 @@ use crate::{
     fs::File,
     header::{
         errno::{self, STR_ERROR},
-        fcntl, pwd, stdlib,
+        fcntl,
+        pthread::RlctMutex,
+        pwd, stdlib,
         string::{self, strlen, strncpy},
         unistd,
     },
@@ -112,7 +114,7 @@ impl<W: crate::io::Write> Writer for LineWriter<W> {
 
 /// This struct gets exposed to the C API.
 pub struct FILE {
-    lock: Mutex<()>,
+    lock: RlctMutex,
 
     file: File,
     // pub for stdio_ext
@@ -535,7 +537,9 @@ pub unsafe extern "C" fn fileno(stream: *mut FILE) -> c_int {
 /// locked
 #[unsafe(no_mangle)]
 pub unsafe extern "C" fn flockfile(file: *mut FILE) {
-    (*file).lock.manual_lock();
+    if let Err(e) = (*file).lock.lock() {
+        println!("RELIBC: flockfile error {}", e)
+    }
 }
 
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/fopen.html>.
@@ -794,7 +798,7 @@ pub unsafe extern "C" fn ftell_locked(stream: &mut FILE) -> off_t {
 /// Try to lock the file. Returns 0 for success, 1 for failure
 #[unsafe(no_mangle)]
 pub unsafe extern "C" fn ftrylockfile(file: *mut FILE) -> c_int {
-    if (*file).lock.manual_try_lock().is_ok() {
+    if (*file).lock.try_lock().is_ok() {
         0
     } else {
         1
@@ -806,7 +810,9 @@ pub unsafe extern "C" fn ftrylockfile(file: *mut FILE) -> c_int {
 /// Unlock the file
 #[unsafe(no_mangle)]
 pub unsafe extern "C" fn funlockfile(file: *mut FILE) {
-    (*file).lock.manual_unlock();
+    if let Err(e) = (*file).lock.unlock() {
+        println!("RELIBC: funlockfile error {}", e)
+    }
 }
 
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/fwrite.html>.
diff --git a/tests/stdio/mutex.c b/tests/stdio/mutex.c
index 3d9be9d8db..dc729d3c5f 100644
--- a/tests/stdio/mutex.c
+++ b/tests/stdio/mutex.c
@@ -1,30 +1,47 @@
 #include <stdio.h>
 #include <stdlib.h>
+#include <pthread.h>
 
 #include "test_helpers.h"
 
-int main(void) {
-    FILE *f = fopen("stdio/stdio.in", "r");
-    ERROR_IF(fopen, f, == NULL);
+FILE *f;
 
-    flockfile(f);
+void* thread_wontlock(void* arg) {
+    (void)arg;
 
-    // Commenting this out should cause a deadlock:
-    // flockfile(f);
+    int result = ftrylockfile(f);
+    UNEXP_IF(ftrylockfile, result, == 0);
 
-    if (!ftrylockfile(f)) {
-        puts("Mutex unlocked but it shouldn't be");
-        exit(EXIT_FAILURE);
-    }
-    funlockfile(f);
-
-    if (ftrylockfile(f)) {
-        puts("Mutex locked but it shouldn't be");
-        exit(EXIT_FAILURE);
-    }
-    if (!ftrylockfile(f)) {
-        puts("Mutex unlocked but it shouldn't be");
-        exit(EXIT_FAILURE);
-    }
-    funlockfile(f);
+    return NULL;
+}
+
+void* thread_willlock(void* arg) {
+    (void)arg;
+
+    int result = ftrylockfile(f);
+    UNEXP_IF(ftrylockfile, result, != 0);
+
+    return NULL;
+}
+
+int main(void) {
+    f = fopen("stdio/stdio.in", "r");
+    ERROR_IF(fopen, f, == NULL);
+    flockfile(f);
+    flockfile(f);
+    thread_willlock(NULL);
+
+    pthread_t thread;
+    for (int i = 1; i <= 3; i++) {
+        pthread_create(&thread, NULL, thread_wontlock, NULL);
+        pthread_join(thread, NULL);
+        funlockfile(f);
+    }
+
+    pthread_create(&thread, NULL, thread_willlock, NULL);
+    pthread_join(thread, NULL);
+
+    // TODO: glibc refuses to quit test without this
+    //       but in relibc, it will result in EPERM
+    // funlockfile(f);
 }
diff --git a/tests/stdio/putc_unlocked.c b/tests/stdio/putc_unlocked.c
index d38a80f32b..693bdafafe 100644
--- a/tests/stdio/putc_unlocked.c
+++ b/tests/stdio/putc_unlocked.c
@@ -11,9 +11,8 @@ int main(void)
     int c = 'c', r = 0;
     r = putc_unlocked(c, fp);
     ERROR_IF(putc_unlocked, r, == EOF);
-    // TODO: hang
-    // r = fflush(fp);
-    // ERROR_IF(fflush, r, == EOF);
+    r = fflush(fp);
+    ERROR_IF(fflush, r, == EOF);
     funlockfile(fp);
     // make sure unlock works
     r = putc(c, fp);