diff --git a/.travis.yml b/.travis.yml
index 99471e800a7..db63faf3f96 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -95,7 +95,7 @@ script:
       linux-amd64-functional)
         docker run --rm \
           --volume=`pwd`:/go/src/go.etcd.io/etcd gcr.io/etcd-development/etcd-test:go${TRAVIS_GO_VERSION} \
-          /bin/bash -c "GO_BUILD_FLAGS='-v -mod=mod' ./build && GOARCH=amd64 PASSES='functional' ./test"
+          /bin/bash -c "GO_BUILD_FLAGS='-v -mod=readonly' ./build && GOARCH=amd64 PASSES='functional' ./test"
         ;;
       linux-amd64-unit)
         docker run --rm \
@@ -107,12 +107,12 @@ script:
           --volume=`pwd`:/go/src/go.etcd.io/etcd gcr.io/etcd-development/etcd-test:go${TRAVIS_GO_VERSION} \
           /bin/bash -c "GOARCH=amd64 PASSES='build' ./test \
             && GOARCH=386 PASSES='build' ./test \
-            && GO_BUILD_FLAGS='-v -mod=mod' GOOS=darwin GOARCH=amd64 ./build \
-            && GO_BUILD_FLAGS='-v -mod=mod' GOOS=windows GOARCH=amd64 ./build \
-            && GO_BUILD_FLAGS='-v -mod=mod' GOARCH=arm ./build \
-            && GO_BUILD_FLAGS='-v -mod=mod' GOARCH=arm64 ./build \
-            && GO_BUILD_FLAGS='-v -mod=mod' GOARCH=ppc64le ./build \
-            && GO_BUILD_FLAGS='-v -mod=mod' GOARCH=s390x ./build"
+            && GO_BUILD_FLAGS='-v -mod=readonly' GOOS=darwin GOARCH=amd64 ./build \
+            && GO_BUILD_FLAGS='-v -mod=readonly' GOOS=windows GOARCH=amd64 ./build \
+            && GO_BUILD_FLAGS='-v -mod=readonly' GOARCH=arm ./build \
+            && GO_BUILD_FLAGS='-v -mod=readonly' GOARCH=arm64 ./build \
+            && GO_BUILD_FLAGS='-v -mod=readonly' GOARCH=ppc64le ./build \
+            && GO_BUILD_FLAGS='-v -mod=readonly' GOARCH=s390x ./build"
         ;;
       linux-amd64-grpcproxy)
         sudo HOST_TMP_DIR=/tmp TEST_OPTS="PASSES='build grpcproxy'" make docker-test
diff --git a/functional/build b/functional/build
index 52ce832ee75..fd121eaf457 100755
--- a/functional/build
+++ b/functional/build
@@ -5,7 +5,7 @@ if ! [[ "$0" =~ "functional/build" ]]; then
   exit 255
 fi
 
-CGO_ENABLED=0 go build -v -mod=mod -installsuffix cgo -ldflags "-s" -o ./bin/etcd-agent ./functional/cmd/etcd-agent
-CGO_ENABLED=0 go build -v -mod=mod -installsuffix cgo -ldflags "-s" -o ./bin/etcd-proxy ./functional/cmd/etcd-proxy
-CGO_ENABLED=0 go build -v -mod=mod -installsuffix cgo -ldflags "-s" -o ./bin/etcd-runner ./functional/cmd/etcd-runner
-CGO_ENABLED=0 go build -v -mod=mod -installsuffix cgo -ldflags "-s" -o ./bin/etcd-tester ./functional/cmd/etcd-tester
+CGO_ENABLED=0 go build -v -installsuffix cgo -ldflags "-s" -o ./bin/etcd-agent ./functional/cmd/etcd-agent
+CGO_ENABLED=0 go build -v -installsuffix cgo -ldflags "-s" -o ./bin/etcd-proxy ./functional/cmd/etcd-proxy
+CGO_ENABLED=0 go build -v -installsuffix cgo -ldflags "-s" -o ./bin/etcd-runner ./functional/cmd/etcd-runner
+CGO_ENABLED=0 go build -v -installsuffix cgo -ldflags "-s" -o ./bin/etcd-tester ./functional/cmd/etcd-tester
diff --git a/test b/test
index 1cf4c247a16..ae3ca76eb0e 100755
--- a/test
+++ b/test
@@ -393,6 +393,8 @@ function shellcheck_pass {
 			echo -e "shellcheck checking failed:\\n${shellcheckResult}"
 			exit 255
 		fi
+  else
+    echo "Shellcheck not found !!! Check: https://github.com/koalaman/shellcheck#installing"
 	fi
 }
 
@@ -627,6 +629,7 @@ function fmt_pass {
 			license_header \
 			receiver_name \
 			commit_title \
+			mod_tidy \
 			; do
 		echo "'$p' started at $(date)"
 		"${p}"_pass "$@"
@@ -684,6 +687,38 @@ function build_pass {
 	GO_BUILD_FLAGS="-v" tools_build
 }
 
+function mod_tidy_pass {
+	# Watch for upstream solution: https://github.com/golang/go/issues/27005
+	local tmpModDir
+	tmpModDir=$(mktemp -d --suffix "etcd-mod")
+  cp "./go.mod" "./go.sum" "${tmpModDir}"
+
+  go mod tidy
+
+  set +e
+  local tmpFileGoModInSync
+  diff -C 5 "${tmpModDir}/go.mod" "./go.mod"
+  tmpFileGoModInSync="$?"
+
+  local tmpFileGoSumInSync
+  diff -C 5 "${tmpModDir}/go.sum" "./go.sum"
+  tmpFileGoSumInSync="$?"
+  set -e
+
+  # Bring back initial state
+  mv "${tmpModDir}/go.mod" "./go.mod"
+  mv "${tmpModDir}/go.sum" "./go.sum"
+
+  if [ "${tmpFileGoModInSync}" -ne 0 ]; then
+		echo "./go.mod is not in sync with 'go mod tidy'"
+		exit 255
+	fi
+	if [ "${tmpFileGoSumInSync}" -ne 0 ]; then
+		echo "./go.sum is not in sync with 'go mod tidy'"
+		exit 255
+	fi
+}
+
 for pass in $PASSES; do
 	echo "Starting '$pass' pass at $(date)"
 	"${pass}"_pass "$@"