diff --git a/tlm-modules/pf-config.h b/tlm-modules/pf-config.h
index 7586975..f4f58ed 100644
--- a/tlm-modules/pf-config.h
+++ b/tlm-modules/pf-config.h
@@ -105,7 +105,7 @@ class PCIExpressCapability: public PCICapability
 		// hardwired to '0' as according to PCI Express Base
 		// specification.
 		//
-		PCIExpressCapSize = PCI_CAP_EXP_ENDPOINT_SIZEOF_V2 + 0x8,
+		PCIExpressCapSize = PCI_CAP_EXP_ENDPOINT_SIZEOF_V2 + 0xA,
 	};
 
 	PCIExpressCapability():
@@ -244,6 +244,7 @@ class PhysFuncConfig
 	{
 		if (m_pciCapTail == 0) {
 			m_pciCapTail = PCI_CONFIG_SIZE - cap_size;
+			assert((m_pciCapTail & 0x3) == 0);  // Dword aligned.
 			SetNextCapPtr(m_pciCapTail);
 			//
 			// Hardwire status 'Capabilities List' to 1
@@ -253,6 +254,7 @@ class PhysFuncConfig
 			uint32_t nextCapPtr = m_pciCapTail + 1;
 
 			m_pciCapTail -= cap_size;
+			assert((m_pciCapTail & 0x3) == 0);  // Dword aligned.
 			m_config[nextCapPtr] = m_pciCapTail;
 		}
 		memcpy(reinterpret_cast<void*>(&m_config[m_pciCapTail]),