diff --git a/include/stdio.h b/include/stdio.h
index 3742f30..3c795fd 100644
--- a/include/stdio.h
+++ b/include/stdio.h
@@ -2,11 +2,13 @@
 #pragma once
 
 #include <cia/def.h>
+#include <cia/sync.h>
 #include <tinyrt.h>
 
 typedef struct FILE FILE;
 struct FILE {
     _RT_File rt_file;
+    Cia_Mutex mutex;
 };
 
 #define EOF (-1)
diff --git a/src/stdlib-file/file.c b/src/stdlib-file/file.c
index 351bbb9..533aa30 100644
--- a/src/stdlib-file/file.c
+++ b/src/stdlib-file/file.c
@@ -5,6 +5,7 @@ FILE *stderr;
 
 static Cia_Pool _page_allocator;
 static Cia_Pool _file_pool;
+static Cia_Mutex _g_pool_mutex;
 
 static void _fileapi_init() {
     cia_pool_create(&_file_pool, cia_allocator_pages(), 0x1000, sizeof(FILE), 16);
@@ -15,6 +16,9 @@ static void _fileapi_init() {
     stdin->rt_file = _rt_file_stdin;
     stdout->rt_file = _rt_file_stdout;
     stderr->rt_file = _rt_file_stderr;
+    cia_mutex_init(&stdin->mutex);
+    cia_mutex_init(&stdout->mutex);
+    cia_mutex_init(&stderr->mutex);
 }
 
 FILE *fopen(char const *restrict filename, char const *restrict mode) {
@@ -30,7 +34,9 @@ FILE *fopen(char const *restrict filename, char const *restrict mode) {
     if(status != _RT_STATUS_OK) {
         return NULL;
     }
-    FILE *file = cia_pool_alloc(&_file_pool);
+    cia_mutex_lock(&_g_pool_mutex);
+    FILE *file = cia_pool_alloc(&_file_pool); // TODO: not thread safe
+    cia_mutex_unlock(&_g_pool_mutex);
     file->rt_file = rt_file;
     return file;
 }
@@ -38,7 +44,9 @@ FILE *fopen(char const *restrict filename, char const *restrict mode) {
 int fgetc(FILE *file) {
     int c = 0;
     u64 bytes_read;
+    cia_mutex_lock(&file->mutex);
     _RT_Status status = _rt_file_read(1, &c, &file->rt_file, &bytes_read);
+    cia_mutex_unlock(&file->mutex);
     if(status == _RT_STATUS_FILE_EOF) {
         return EOF;
     }
@@ -50,7 +58,9 @@ int fgetc(FILE *file) {
 
 int fputc(int c, FILE *file) {
     u64 bytes_written;
+    cia_mutex_lock(&file->mutex);
     _RT_Status status = _rt_file_write(&file->rt_file, 1, &c, &bytes_written);
+    cia_mutex_unlock(&file->mutex);
     if(status != _RT_STATUS_OK) {
         return EOF;
     }
@@ -59,7 +69,9 @@ int fputc(int c, FILE *file) {
 
 size_t fread(void *restrict buf, size_t size, size_t count, FILE *restrict file) {
     u64 bytes_read;
+    cia_mutex_lock(&file->mutex);
     _RT_Status status = _rt_file_read(size*count, buf, &file->rt_file, &bytes_read);
+    cia_mutex_unlock(&file->mutex);
     if(status != _RT_STATUS_OK) {
         return 0;
     }
@@ -68,7 +80,9 @@ size_t fread(void *restrict buf, size_t size, size_t count, FILE *restrict file)
 
 size_t fwrite(void const *restrict buf, size_t size, size_t count, FILE *restrict file) {
     u64 bytes_written;
+    cia_mutex_lock(&file->mutex);
     _RT_Status status = _rt_file_write(&file->rt_file, size*count, (void *)buf, &bytes_written);
+    cia_mutex_unlock(&file->mutex);
     if(status != _RT_STATUS_OK) {
         return 0;
     }
@@ -80,6 +94,8 @@ int fclose(FILE *file) {
     if(status != _RT_STATUS_OK) {
         return EOF;
     }
+    cia_mutex_lock(&_g_pool_mutex);
     cia_pool_free(&_file_pool, file);
+    cia_mutex_unlock(&_g_pool_mutex);
     return 0;
 }