diff --git a/hw/phb4.c b/hw/phb4.c
index 83c0fc0..06ad18f 100644
--- a/hw/phb4.c
+++ b/hw/phb4.c
@@ -225,6 +225,10 @@
 
 static uint64_t phb4_read_reg(struct phb4 *p, uint32_t offset)
 {
+	/* No register accesses are permitted while in reset */
+	if (p->flags & PHB4_ETU_IN_RESET)
+		return -1ull;
+
 	if (p->flags & PHB4_CFG_USE_ASB)
 		return phb4_read_reg_asb(p, offset);
 	else
@@ -233,6 +237,10 @@
 
 static void phb4_write_reg(struct phb4 *p, uint32_t offset, uint64_t val)
 {
+	/* No register accesses are permitted while in reset */
+	if (p->flags & PHB4_ETU_IN_RESET)
+		return;
+
 	if (p->flags & PHB4_CFG_USE_ASB)
 		phb4_write_reg_asb(p, offset, val);
 	else
@@ -3268,6 +3276,7 @@
 		phb4_err_clear(p);
 
 		/* Actual reset */
+		p->flags |= PHB4_ETU_IN_RESET;
 		xscom_write(p->chip_id, p->pci_stk_xscom + XPEC_PCI_STK_ETU_RESET,
 			    0x8000000000000000UL);
 
@@ -3321,6 +3330,7 @@
 			/* Clear PHB from reset */
 			xscom_write(p->chip_id,
 				    p->pci_stk_xscom + XPEC_PCI_STK_ETU_RESET, 0x0);
+			p->flags &= ~PHB4_ETU_IN_RESET;
 
 			pci_slot_set_state(slot, PHB4_SLOT_CRESET_REINIT);
 			/* After lifting PHB reset, wait while logic settles */
diff --git a/include/phb4.h b/include/phb4.h
index c52a840..dc84fca 100644
--- a/include/phb4.h
+++ b/include/phb4.h
@@ -166,6 +166,7 @@
 #define PHB4_CFG_BLOCKED	0x00000004
 #define PHB4_CAPP_RECOVERY	0x00000008
 #define PHB4_CAPP_DISABLE	0x00000010
+#define PHB4_ETU_IN_RESET	0x00000020
 
 struct phb4 {
 	unsigned int		index;	    /* 0..5 index inside p9 */