diff --git a/products/compute/terraform.yaml b/products/compute/terraform.yaml
index ef1aad05d1f9..2619874a0bb0 100644
--- a/products/compute/terraform.yaml
+++ b/products/compute/terraform.yaml
@@ -1484,6 +1484,9 @@ overrides: !ruby/object:Overrides::ResourceOverrides
         vars:
           router_name: "my-router"
           network_name: "my-network"
+    custom_code: !ruby/object:Provider::Terraform::CustomCode
+      constants: templates/terraform/constants/router.go.erb
+      resource_definition: templates/terraform/resource_definition/router.go.erb
     properties:
       id: !ruby/object:Overrides::Terraform::PropertyOverride
         exclude: true
diff --git a/templates/terraform/constants/router.go.erb b/templates/terraform/constants/router.go.erb
new file mode 100644
index 000000000000..77b7bbdb3280
--- /dev/null
+++ b/templates/terraform/constants/router.go.erb
@@ -0,0 +1,31 @@
+<%- # the license inside this block applies to this file
+	# Copyright 2020 Google Inc.
+	# Licensed under the Apache License, Version 2.0 (the "License");
+	# you may not use this file except in compliance with the License.
+	# You may obtain a copy of the License at
+	#
+	#     http://www.apache.org/licenses/LICENSE-2.0
+	#
+	# Unless required by applicable law or agreed to in writing, software
+	# distributed under the License is distributed on an "AS IS" BASIS,
+	# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+	# See the License for the specific language governing permissions and
+	# limitations under the License.
+-%>
+// customizeDiff func for additional checks on google_compute_router properties:
+func resourceComputeRouterCustomDiff(diff *schema.ResourceDiff, meta interface{}) error {
+
+	block := diff.Get("bgp.0").(map[string]interface{})
+	advertiseMode := block["advertise_mode"]
+	advertisedGroups := block["advertised_groups"].([]interface{})
+	advertisedIPRanges := block["advertised_ip_ranges"].([]interface{})
+
+	if advertiseMode == "DEFAULT" && len(advertisedGroups) != 0 {
+		return fmt.Errorf("Error in bgp: advertised_groups cannot be specified when using advertise_mode DEFAULT")
+	}
+	if advertiseMode == "DEFAULT" && len(advertisedIPRanges) != 0 {
+		return fmt.Errorf("Error in bgp: advertised_ip_ranges cannot be specified when using advertise_mode DEFAULT")
+	}
+
+	return nil
+}
diff --git a/templates/terraform/resource_definition/router.go.erb b/templates/terraform/resource_definition/router.go.erb
new file mode 100644
index 000000000000..2dbbafaa43d1
--- /dev/null
+++ b/templates/terraform/resource_definition/router.go.erb
@@ -0,0 +1,15 @@
+<%# The license inside this block applies to this file.
+	# Copyright 2020 Google Inc.
+	# Licensed under the Apache License, Version 2.0 (the "License");
+	# you may not use this file except in compliance with the License.
+	# You may obtain a copy of the License at
+	#
+	#     http://www.apache.org/licenses/LICENSE-2.0
+	#
+	# Unless required by applicable law or agreed to in writing, software
+	# distributed under the License is distributed on an "AS IS" BASIS,
+	# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+	# See the License for the specific language governing permissions and
+	# limitations under the License.
+-%>
+CustomizeDiff: resourceComputeRouterCustomDiff,