diff --git a/hw/arm/smmu-common.c b/hw/arm/smmu-common.c
index 3098915d07c98e87f1386d7e26274fc252985cf0..55c75d65d2e44d2d2981482584f648c4728cd124 100644
--- a/hw/arm/smmu-common.c
+++ b/hw/arm/smmu-common.c
@@ -351,7 +351,7 @@ IOMMUMemoryRegion *smmu_iommu_mr(SMMUState *s, uint32_t sid)
     bus_n = PCI_BUS_NUM(sid);
     smmu_bus = smmu_find_smmu_pcibus(s, bus_n);
     if (smmu_bus) {
-        devfn = sid & 0x7;
+        devfn = SMMU_PCI_DEVFN(sid);
         smmu = smmu_bus->pbdev[devfn];
         if (smmu) {
             return &smmu->iommu;
diff --git a/include/hw/arm/smmu-common.h b/include/hw/arm/smmu-common.h
index 50e2912a95efd271b2c344ec10aeac3701f45338..b07cadd0ef9373f7d0994057d312ca9208b965dd 100644
--- a/include/hw/arm/smmu-common.h
+++ b/include/hw/arm/smmu-common.h
@@ -24,6 +24,7 @@
 
 #define SMMU_PCI_BUS_MAX      256
 #define SMMU_PCI_DEVFN_MAX    256
+#define SMMU_PCI_DEVFN(sid)   (sid & 0xFF)
 
 #define SMMU_MAX_VA_BITS      48