diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index fdf5ad19ee..970efbb13c 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -11064,6 +11064,7 @@ virDomainNetDefParseXML(virDomainXMLOptionPtr xmlopt,
         }
     } else {
         virDomainNetGenerateMAC(xmlopt, &def->mac);
+        def->mac_generated = true;
     }
 
     if (devaddr) {
@@ -16338,7 +16339,7 @@ virDomainNetFindIdx(virDomainDefPtr def, virDomainNetDefPtr net)
     size_t i;
     int matchidx = -1;
     char mac[VIR_MAC_STRING_BUFLEN];
-    bool MACAddrSpecified = !net->mac.generated;
+    bool MACAddrSpecified = !net->mac_generated;
     bool PCIAddrSpecified = virDomainDeviceAddressIsValid(&net->info,
                                                           VIR_DOMAIN_DEVICE_ADDRESS_TYPE_PCI);
 
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index bf4ff64739..117efb1d1d 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -966,6 +966,7 @@ struct _virDomainActualNetDef {
 struct _virDomainNetDef {
     virDomainNetType type;
     virMacAddr mac;
+    bool mac_generated; /* true if mac was *just now* auto-generated by libvirt */
     char *model;
     union {
         struct {
diff --git a/src/util/virmacaddr.c b/src/util/virmacaddr.c
index 409fdc34d5..7afe032b9c 100644
--- a/src/util/virmacaddr.c
+++ b/src/util/virmacaddr.c
@@ -107,7 +107,6 @@ void
 virMacAddrSet(virMacAddrPtr dst, const virMacAddr *src)
 {
     memcpy(dst, src, sizeof(*src));
-    dst->generated = false;
 }
 
 /**
@@ -121,7 +120,6 @@ void
 virMacAddrSetRaw(virMacAddrPtr dst, const unsigned char src[VIR_MAC_BUFLEN])
 {
     memcpy(dst->addr, src, VIR_MAC_BUFLEN);
-    dst->generated = false;
 }
 
 /**
@@ -151,7 +149,6 @@ virMacAddrParse(const char* str, virMacAddrPtr addr)
 {
     size_t i;
 
-    addr->generated = false;
     errno = 0;
     for (i = 0; i < VIR_MAC_BUFLEN; i++) {
         char *end_ptr;
@@ -220,7 +217,6 @@ virMacAddrParseHex(const char *str, virMacAddrPtr addr)
         str[VIR_MAC_HEXLEN])
         return -1;
 
-    addr->generated = false;
     for (i = 0; i < VIR_MAC_BUFLEN; i++)
         addr->addr[i] = (virHexToBin(str[2 * i]) << 4 |
                          virHexToBin(str[2 * i + 1]));
@@ -236,7 +232,6 @@ void virMacAddrGenerate(const unsigned char prefix[VIR_MAC_PREFIX_BUFLEN],
     addr->addr[3] = virRandomBits(8);
     addr->addr[4] = virRandomBits(8);
     addr->addr[5] = virRandomBits(8);
-    addr->generated = true;
 }
 
 /* The low order bit of the first byte is the "multicast" bit. */
diff --git a/src/util/virmacaddr.h b/src/util/virmacaddr.h
index ef4285d639..d0dd4a45c6 100644
--- a/src/util/virmacaddr.h
+++ b/src/util/virmacaddr.h
@@ -36,9 +36,14 @@ typedef virMacAddr *virMacAddrPtr;
 
 struct _virMacAddr {
     unsigned char addr[VIR_MAC_BUFLEN];
-    bool generated; /* True if MAC address was autogenerated,
-                       false otherwise. */
 };
+/* This struct is used as a part of a larger struct that is
+ * overlaid on an ethernet packet captured with libpcap, so it
+ * must not have any extra members added - it must remain exactly
+ * 6 bytes in length.
+ */
+verify(sizeof(struct _virMacAddr) == 6);
+
 
 int virMacAddrCompare(const char *mac1, const char *mac2);
 int virMacAddrCmp(const virMacAddr *mac1, const virMacAddr *mac2);
diff --git a/tests/bhyveargv2xmlmock.c b/tests/bhyveargv2xmlmock.c
index dd25f4e13a..1f08bebb7b 100644
--- a/tests/bhyveargv2xmlmock.c
+++ b/tests/bhyveargv2xmlmock.c
@@ -16,7 +16,6 @@ virMacAddrGenerate(const unsigned char prefix[VIR_MAC_PREFIX_BUFLEN],
     addr->addr[3] = 0;
     addr->addr[4] = 0;
     addr->addr[5] = 0;
-    addr->generated = true;
 }
 
 int