diff --git a/reactos/ntoskrnl/mm/section.c b/reactos/ntoskrnl/mm/section.c
index ef4ae6f62b3..a4060dc1cb1 100644
--- a/reactos/ntoskrnl/mm/section.c
+++ b/reactos/ntoskrnl/mm/section.c
@@ -4911,8 +4911,12 @@ MmUnmapViewInSystemSpace (IN PVOID MappedBase)
    DPRINT("MmUnmapViewInSystemSpace() called\n");
 
    AddressSpace = MmGetKernelAddressSpace();
+   
+   MmLockAddressSpace(AddressSpace);
 
    Status = MmUnmapViewOfSegment(AddressSpace, MappedBase);
+   
+   MmUnlockAddressSpace(AddressSpace);
 
    return Status;
 }