diff --git a/reactos/hal/halx86/generic/fmutex.c b/reactos/hal/halx86/generic/fmutex.c
index 77da8d8564d..2ada2b41925 100644
--- a/reactos/hal/halx86/generic/fmutex.c
+++ b/reactos/hal/halx86/generic/fmutex.c
@@ -84,6 +84,7 @@ ExTryToAcquireFastMutex(PFAST_MUTEX FastMutex)
     {
         /* We have, set us as owners */
         FastMutex->Owner = KeGetCurrentThread();
+        FastMutex->OldIrql = OldIrql;
         return TRUE;
     }
     else
diff --git a/reactos/ntoskrnl/ex/fmutex.c b/reactos/ntoskrnl/ex/fmutex.c
index 689d8365e30..6b229e2cc07 100644
--- a/reactos/ntoskrnl/ex/fmutex.c
+++ b/reactos/ntoskrnl/ex/fmutex.c
@@ -191,6 +191,7 @@ ExTryToAcquireFastMutex(PFAST_MUTEX FastMutex)
     {
         /* We have, set us as owners */
         FastMutex->Owner = KeGetCurrentThread();
+        FastMutex->OldIrql = OldIrql;
         return TRUE;
     }
     else