diff --git a/.travis.yml b/.travis.yml
index 5a54a241..34539ba4 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,9 +9,12 @@ env:
   - GO111MODULE=on
 
 script:
+  - go vet ./...
   - go build ./...
   - go install github.com/golang/mock/mockgen
+  - GO111MODULE=off go get -u golang.org/x/lint/golint
   - ./ci/check_go_fmt.sh
+  - ./ci/check_go_lint.sh
   - ./ci/check_go_generate.sh
   - ./ci/check_go_mod.sh
   - go test -v ./...
diff --git a/ci/check_go_lint.sh b/ci/check_go_lint.sh
new file mode 100755
index 00000000..78333075
--- /dev/null
+++ b/ci/check_go_lint.sh
@@ -0,0 +1,17 @@
+#!/bin/bash
+# This script is used by CI to check if the code passes golint.
+
+set -u
+
+if ! command -v golint >/dev/null; then
+    echo "error: golint not found; go get -u golang.org/x/lint/golint" >&2
+    exit 1
+fi
+
+GOLINT_OUTPUT=$(IFS=$'\n'; golint ./... | grep -v "mockgen/internal/.*\|sample/.*")
+if [[ -n "${GOLINT_OUTPUT}" ]]; then
+    echo "${GOLINT_OUTPUT}"
+    echo
+    echo "The go source files aren't passing golint."
+    exit 1
+fi
diff --git a/ci/check_go_mod.sh b/ci/check_go_mod.sh
index 56e79127..262f74c5 100755
--- a/ci/check_go_mod.sh
+++ b/ci/check_go_mod.sh
@@ -7,6 +7,7 @@ go mod tidy
 
 if [ ! -z "$(git status --porcelain)" ]; then
     git status
+    git diff
     echo
     echo "The go.mod is not up to date."
     exit 1
diff --git a/gomock/call.go b/gomock/call.go
index 826f45d2..7bdeab94 100644
--- a/gomock/call.go
+++ b/gomock/call.go
@@ -389,7 +389,7 @@ func (c *Call) matches(args []interface{}) error {
 
 	// Check that the call is not exhausted.
 	if c.exhausted() {
-		return fmt.Errorf("Expected call at %s has already been called the max number of times.", c.origin)
+		return fmt.Errorf("expected call at %s has already been called the max number of times", c.origin)
 	}
 
 	return nil
diff --git a/mockgen/model/model.go b/mockgen/model/model.go
index 8113e3d3..b93e062a 100644
--- a/mockgen/model/model.go
+++ b/mockgen/model/model.go
@@ -33,6 +33,7 @@ type Package struct {
 	DotImports []string
 }
 
+// Print writes the package name and its exported interfaces.
 func (pkg *Package) Print(w io.Writer) {
 	fmt.Fprintf(w, "package %s\n", pkg.Name)
 	for _, intf := range pkg.Interfaces {
@@ -55,6 +56,7 @@ type Interface struct {
 	Methods []*Method
 }
 
+// Print writes the interface name and its methods.
 func (intf *Interface) Print(w io.Writer) {
 	fmt.Fprintf(w, "interface %s\n", intf.Name)
 	for _, m := range intf.Methods {
@@ -75,6 +77,7 @@ type Method struct {
 	Variadic *Parameter // may be nil
 }
 
+// Print writes the method name and its signature.
 func (m *Method) Print(w io.Writer) {
 	fmt.Fprintf(w, "  - method %s\n", m.Name)
 	if len(m.In) > 0 {
@@ -113,6 +116,7 @@ type Parameter struct {
 	Type Type
 }
 
+// Print writes a method parameter.
 func (p *Parameter) Print(w io.Writer) {
 	n := p.Name
 	if n == "" {
@@ -183,6 +187,7 @@ func (ct *ChanType) addImports(im map[string]bool) { ct.Type.addImports(im) }
 // ChanDir is a channel direction.
 type ChanDir int
 
+// Constants for channel directions.
 const (
 	RecvDir ChanDir = 1
 	SendDir ChanDir = 2
@@ -255,9 +260,9 @@ func (nt *NamedType) String(pm map[string]string, pkgOverride string) string {
 	prefix := pm[nt.Package]
 	if prefix != "" {
 		return prefix + "." + nt.Type
-	} else {
-		return nt.Type
 	}
+
+	return nt.Type
 }
 func (nt *NamedType) addImports(im map[string]bool) {
 	if nt.Package != "" {
@@ -283,6 +288,8 @@ func (pt PredeclaredType) addImports(im map[string]bool)
 
 // The following code is intended to be called by the program generated by ../reflect.go.
 
+// InterfaceFromInterfaceType returns a pointer to an interface for the
+// given reflection interface type.
 func InterfaceFromInterfaceType(it reflect.Type) (*Interface, error) {
 	if it.Kind() != reflect.Interface {
 		return nil, fmt.Errorf("%v is not an interface", it)