diff --git a/arch/sparc/mm/io-unit.c b/arch/sparc/mm/io-unit.c
index 42c1c70..2bb1309 100644
--- a/arch/sparc/mm/io-unit.c
+++ b/arch/sparc/mm/io-unit.c
@@ -64,6 +64,7 @@
 	
 	sbus->iommu = (struct iommu_struct *)iounit;
 	iounit->page_table = xpt;
+	spin_lock_init(&iounit->lock);
 	
 	for (xptend = iounit->page_table + (16 * PAGE_SIZE) / sizeof(iopte_t);
 	     xpt < xptend;)