diff --git a/kernel/src/sys/setitimer.cpp b/kernel/src/sys/setitimer.cpp
index 199eacef..d3b03fa2 100644
--- a/kernel/src/sys/setitimer.cpp
+++ b/kernel/src/sys/setitimer.cpp
@@ -118,7 +118,6 @@ Result<u64> sys_timer_create(Registers*, SyscallArgs args)
     if (ksevp.sigev_signo <= 0 || ksevp.sigev_signo > NSIG) return err(EINVAL);
 
     int id = TRY(current->allocate_timerid());
-    current->posix_timers[id] = Timer {};
 
     Timer* timer = current->posix_timers[id].value_ptr();
     timer->signo = ksevp.sigev_signo;
diff --git a/kernel/src/thread/Thread.cpp b/kernel/src/thread/Thread.cpp
index 77b7f42a..1d56b822 100644
--- a/kernel/src/thread/Thread.cpp
+++ b/kernel/src/thread/Thread.cpp
@@ -61,10 +61,15 @@ Result<FileDescriptor*> Thread::resolve_fd(int fd)
 
 Result<int> Thread::allocate_timerid()
 {
+    ScopedMutexLock lock(posix_timer_mutex);
+
     for (int i = 0; i < MAX_POSIX_TIMERS; i++)
     {
-        // FIXME: Possible race condition, this should be used alongside a mutex.
-        if (!posix_timers[i].has_value()) { return i; }
+        if (!posix_timers[i].has_value())
+        {
+            posix_timers[i] = Timer {};
+            return i;
+        }
     }
 
     return err(EMFILE);
diff --git a/kernel/src/thread/Thread.h b/kernel/src/thread/Thread.h
index eb185949..2d19cc69 100644
--- a/kernel/src/thread/Thread.h
+++ b/kernel/src/thread/Thread.h
@@ -3,6 +3,7 @@
 #include "arch/MMU.h"
 #include "fs/OpenFileDescription.h"
 #include "fs/VFS.h"
+#include "lib/Mutex.h"
 #include "memory/AddressSpace.h"
 #include <bits/signal.h>
 #include <luna/Bitset.h>
@@ -109,6 +110,7 @@ struct Thread : public LinkedListNode<Thread>
     Clock profiling_clock;
 
     Option<Timer> posix_timers[MAX_POSIX_TIMERS];
+    Mutex posix_timer_mutex;
 
     Result<int> allocate_timerid();
     Result<Timer*> resolve_timerid(int id);