diff --git a/src/network/bridge_driver.c b/src/network/bridge_driver.c
index 6d80818e40..b3ca5b8a15 100644
--- a/src/network/bridge_driver.c
+++ b/src/network/bridge_driver.c
@@ -1320,11 +1320,27 @@ networkDnsmasqConfContents(virNetworkObjPtr obj,
                 !(eaddr = virSocketAddrFormat(&ipdef->ranges[r].end)))
                 goto cleanup;
 
-            virBufferAsprintf(&configbuf, "dhcp-range=%s,%s",
-                              saddr, eaddr);
-            if (VIR_SOCKET_ADDR_IS_FAMILY(&ipdef->address, AF_INET6))
-                virBufferAsprintf(&configbuf, ",%d", prefix);
-            virBufferAddLit(&configbuf, "\n");
+            if (VIR_SOCKET_ADDR_IS_FAMILY(&ipdef->address, AF_INET6)) {
+               virBufferAsprintf(&configbuf, "dhcp-range=%s,%s,%d\n",
+                                 saddr, eaddr, prefix);
+            } else {
+                /* IPv4 - dnsmasq requires a netmask rather than prefix */
+                virSocketAddr netmask;
+                VIR_AUTOFREE(char *) netmaskStr = NULL;
+
+                if (virSocketAddrPrefixToNetmask(prefix, &netmask, AF_INET) < 0) {
+                    virReportError(VIR_ERR_INTERNAL_ERROR,
+                                   _("Failed to translate bridge '%s' "
+                                     "prefix %d to netmask"),
+                                   def->bridge, prefix);
+                    goto cleanup;
+                }
+
+                if (!(netmaskStr = virSocketAddrFormat(&netmask)))
+                    goto cleanup;
+                virBufferAsprintf(&configbuf, "dhcp-range=%s,%s,%s\n",
+                                  saddr, eaddr, netmaskStr);
+            }
 
             VIR_FREE(saddr);
             VIR_FREE(eaddr);
diff --git a/tests/networkxml2confdata/dhcp6-nat-network.conf b/tests/networkxml2confdata/dhcp6-nat-network.conf
index d1058df3b6..536974e508 100644
--- a/tests/networkxml2confdata/dhcp6-nat-network.conf
+++ b/tests/networkxml2confdata/dhcp6-nat-network.conf
@@ -8,7 +8,7 @@ strict-order
 except-interface=lo
 bind-dynamic
 interface=virbr0
-dhcp-range=192.168.122.2,192.168.122.254
+dhcp-range=192.168.122.2,192.168.122.254,255.255.255.0
 dhcp-no-override
 dhcp-authoritative
 dhcp-range=2001:db8:ac10:fd01::1:10,2001:db8:ac10:fd01::1:ff,64
diff --git a/tests/networkxml2confdata/isolated-network.conf b/tests/networkxml2confdata/isolated-network.conf
index ce4a59f6c1..693a83d9a0 100644
--- a/tests/networkxml2confdata/isolated-network.conf
+++ b/tests/networkxml2confdata/isolated-network.conf
@@ -10,7 +10,7 @@ bind-interfaces
 listen-address=192.168.152.1
 dhcp-option=3
 no-resolv
-dhcp-range=192.168.152.2,192.168.152.254
+dhcp-range=192.168.152.2,192.168.152.254,255.255.255.0
 dhcp-no-override
 dhcp-authoritative
 dhcp-lease-max=253
diff --git a/tests/networkxml2confdata/nat-network-dns-srv-record-minimal.conf b/tests/networkxml2confdata/nat-network-dns-srv-record-minimal.conf
index f35ea1d5d4..0b2ca6f5aa 100644
--- a/tests/networkxml2confdata/nat-network-dns-srv-record-minimal.conf
+++ b/tests/networkxml2confdata/nat-network-dns-srv-record-minimal.conf
@@ -13,7 +13,7 @@ listen-address=fc00:db8:ac10:fe01::1
 listen-address=fc00:db8:ac10:fd01::1
 listen-address=10.24.10.1
 srv-host=_name._tcp
-dhcp-range=192.168.122.2,192.168.122.254
+dhcp-range=192.168.122.2,192.168.122.254,255.255.255.0
 dhcp-no-override
 dhcp-authoritative
 dhcp-lease-max=253
diff --git a/tests/networkxml2confdata/nat-network-dns-srv-record.conf b/tests/networkxml2confdata/nat-network-dns-srv-record.conf
index af1ed70758..a18c09aaa7 100644
--- a/tests/networkxml2confdata/nat-network-dns-srv-record.conf
+++ b/tests/networkxml2confdata/nat-network-dns-srv-record.conf
@@ -15,7 +15,7 @@ srv-host=_name4._tcp.test4.com,test4.example.com,4444
 srv-host=_name5._udp,test5.example.com,1,55,555
 srv-host=_name6._tcp.test6.com,test6.example.com,6666,0,666
 srv-host=_name7._tcp.test7.com,test7.example.com,1,0,777
-dhcp-range=192.168.122.2,192.168.122.254
+dhcp-range=192.168.122.2,192.168.122.254,255.255.255.0
 dhcp-no-override
 dhcp-authoritative
 dhcp-lease-max=253
diff --git a/tests/networkxml2confdata/nat-network-dns-txt-record.conf b/tests/networkxml2confdata/nat-network-dns-txt-record.conf
index 7f560fbb5c..735c261c01 100644
--- a/tests/networkxml2confdata/nat-network-dns-txt-record.conf
+++ b/tests/networkxml2confdata/nat-network-dns-txt-record.conf
@@ -9,7 +9,7 @@ except-interface=lo
 bind-dynamic
 interface=virbr0
 txt-record=example,example value
-dhcp-range=192.168.122.2,192.168.122.254
+dhcp-range=192.168.122.2,192.168.122.254,255.255.255.0
 dhcp-no-override
 dhcp-authoritative
 dhcp-lease-max=253
diff --git a/tests/networkxml2confdata/nat-network-mtu.conf b/tests/networkxml2confdata/nat-network-mtu.conf
index 91b574b964..1dd4754f2a 100644
--- a/tests/networkxml2confdata/nat-network-mtu.conf
+++ b/tests/networkxml2confdata/nat-network-mtu.conf
@@ -8,7 +8,7 @@ strict-order
 except-interface=lo
 bind-dynamic
 interface=virbr0
-dhcp-range=192.168.122.2,192.168.122.254
+dhcp-range=192.168.122.2,192.168.122.254,255.255.255.0
 dhcp-no-override
 dhcp-authoritative
 dhcp-lease-max=253
diff --git a/tests/networkxml2confdata/nat-network-name-with-quotes.conf b/tests/networkxml2confdata/nat-network-name-with-quotes.conf
index 36e11d17b9..1b06de3066 100644
--- a/tests/networkxml2confdata/nat-network-name-with-quotes.conf
+++ b/tests/networkxml2confdata/nat-network-name-with-quotes.conf
@@ -13,7 +13,7 @@ listen-address=fc00:db8:ac10:fe01::1
 listen-address=fc00:db8:ac10:fd01::1
 listen-address=10.24.10.1
 srv-host=_name._tcp
-dhcp-range=192.168.122.2,192.168.122.254
+dhcp-range=192.168.122.2,192.168.122.254,255.255.255.0
 dhcp-no-override
 dhcp-authoritative
 dhcp-lease-max=253
diff --git a/tests/networkxml2confdata/nat-network.conf b/tests/networkxml2confdata/nat-network.conf
index a3c8b102d3..873a360acc 100644
--- a/tests/networkxml2confdata/nat-network.conf
+++ b/tests/networkxml2confdata/nat-network.conf
@@ -8,7 +8,7 @@ strict-order
 except-interface=lo
 bind-dynamic
 interface=virbr0
-dhcp-range=192.168.122.2,192.168.122.254
+dhcp-range=192.168.122.2,192.168.122.254,255.255.255.0
 dhcp-no-override
 dhcp-authoritative
 dhcp-lease-max=253
diff --git a/tests/networkxml2confdata/netboot-network.conf b/tests/networkxml2confdata/netboot-network.conf
index b554a5456c..99272b9d68 100644
--- a/tests/networkxml2confdata/netboot-network.conf
+++ b/tests/networkxml2confdata/netboot-network.conf
@@ -10,7 +10,7 @@ expand-hosts
 except-interface=lo
 bind-interfaces
 listen-address=192.168.122.1
-dhcp-range=192.168.122.2,192.168.122.254
+dhcp-range=192.168.122.2,192.168.122.254,255.255.255.0
 dhcp-no-override
 dhcp-authoritative
 enable-tftp
diff --git a/tests/networkxml2confdata/netboot-proxy-network.conf b/tests/networkxml2confdata/netboot-proxy-network.conf
index afb4033f7e..fb0a20cff4 100644
--- a/tests/networkxml2confdata/netboot-proxy-network.conf
+++ b/tests/networkxml2confdata/netboot-proxy-network.conf
@@ -10,7 +10,7 @@ expand-hosts
 except-interface=lo
 bind-interfaces
 listen-address=192.168.122.1
-dhcp-range=192.168.122.2,192.168.122.254
+dhcp-range=192.168.122.2,192.168.122.254,255.255.255.0
 dhcp-no-override
 dhcp-authoritative
 dhcp-boot=pxeboot.img,,10.20.30.40
diff --git a/tests/networkxml2confdata/ptr-domains-auto.conf b/tests/networkxml2confdata/ptr-domains-auto.conf
index 7f1a393dd5..86701c4ddf 100644
--- a/tests/networkxml2confdata/ptr-domains-auto.conf
+++ b/tests/networkxml2confdata/ptr-domains-auto.conf
@@ -10,7 +10,7 @@ local=/1.0.e.f.0.1.c.a.8.b.d.0.1.0.0.2.ip6.arpa/
 except-interface=lo
 bind-dynamic
 interface=virbr0
-dhcp-range=192.168.122.2,192.168.122.254
+dhcp-range=192.168.122.2,192.168.122.254,255.255.255.0
 dhcp-no-override
 dhcp-authoritative
 dhcp-lease-max=253