diff --git a/src/parse.c b/src/parse.c
index 426d1673e..5744ced97 100644
--- a/src/parse.c
+++ b/src/parse.c
@@ -49,9 +49,7 @@
 #define vxlan_offset(field) GUINT_TO_POINTER(offsetof(NetplanVxlan, field))
 
 /* convenience macro to avoid strdup'ing a string into a field if it's already set. */
-#define set_str_if_null(dst, src) { if (dst) {\
-    g_assert_cmpstr(src, ==, dst); \
-} else { \
+#define set_str_if_null(dst, src) { if (dst == NULL) {\
     dst = g_strdup(src); \
 } }
 
@@ -1455,6 +1453,10 @@ handle_gateway4(NetplanParser* npp, yaml_node_t* node, __unused const void* _, G
 {
     if (!is_ip4_address(scalar(node)))
         return yaml_error(npp, node, error, "invalid IPv4 address '%s'", scalar(node));
+    if (npp->current.netdef->gateway4) {
+        g_free(npp->current.netdef->gateway4);
+        npp->current.netdef->gateway4 = NULL;
+    }
     set_str_if_null(npp->current.netdef->gateway4, scalar(node));
     mark_data_as_dirty(npp, &npp->current.netdef->gateway4);
     g_warning("`gateway4` has been deprecated, use default routes instead.\n"
@@ -1467,6 +1469,10 @@ handle_gateway6(NetplanParser* npp, yaml_node_t* node, __unused const void* _, G
 {
     if (!is_ip6_address(scalar(node)))
         return yaml_error(npp, node, error, "invalid IPv6 address '%s'", scalar(node));
+    if (npp->current.netdef->gateway6) {
+        g_free(npp->current.netdef->gateway6);
+        npp->current.netdef->gateway6 = NULL;
+    }
     set_str_if_null(npp->current.netdef->gateway6, scalar(node));
     mark_data_as_dirty(npp, &npp->current.netdef->gateway6);
     g_warning("`gateway6` has been deprecated, use default routes instead.\n"
diff --git a/tests/generator/test_common.py b/tests/generator/test_common.py
index 785f6f426..2128e5875 100644
--- a/tests/generator/test_common.py
+++ b/tests/generator/test_common.py
@@ -1825,3 +1825,43 @@ def test_wifi_access_points_overwriting(self):
   psk="bbbbbbbb"
 }
 """)
+
+    def test_gateway6_redefinition_works(self):
+        self.generate('''network:
+  version: 2
+  ethernets:
+    engreen:
+      addresses: [2001:FFfe::1/62]
+      gateway6: 2001:FFfe::2''', confs={'b': '''network:
+  ethernets:
+    engreen:
+      gateway6: 2001:FFfe::34'''}, expect_fail=False)
+
+        self.assert_networkd({'engreen.network': '''[Match]
+Name=engreen
+
+[Network]
+LinkLocalAddressing=ipv6
+Address=2001:FFfe::1/62
+Gateway=2001:FFfe::34
+'''})
+
+    def test_gateway4_redefinition_works(self):
+        self.generate('''network:
+  version: 2
+  ethernets:
+    engreen:
+      addresses: [192.168.0.1/24]
+      gateway4: 192.168.0.123''', confs={'b': '''network:
+  ethernets:
+    engreen:
+      gateway4: 192.168.0.254'''}, expect_fail=False)
+
+        self.assert_networkd({'engreen.network': '''[Match]
+Name=engreen
+
+[Network]
+LinkLocalAddressing=ipv6
+Address=192.168.0.1/24
+Gateway=192.168.0.254
+'''})