diff --git a/github/github-accessors.go b/github/github-accessors.go
index 073a3b9cea9..6e118bdec14 100644
--- a/github/github-accessors.go
+++ b/github/github-accessors.go
@@ -3612,6 +3612,14 @@ func (i *Invitation) GetTeamCount() int {
 	return *i.TeamCount
 }
 
+// GetActiveLockReason returns the ActiveLockReason field if it's non-nil, zero value otherwise.
+func (i *Issue) GetActiveLockReason() string {
+	if i == nil || i.ActiveLockReason == nil {
+		return ""
+	}
+	return *i.ActiveLockReason
+}
+
 // GetAssignee returns the Assignee field.
 func (i *Issue) GetAssignee() *User {
 	if i == nil {
@@ -4012,6 +4020,14 @@ func (i *IssueEvent) GetLabel() *Label {
 	return i.Label
 }
 
+// GetLockReason returns the LockReason field if it's non-nil, zero value otherwise.
+func (i *IssueEvent) GetLockReason() string {
+	if i == nil || i.LockReason == nil {
+		return ""
+	}
+	return *i.LockReason
+}
+
 // GetMilestone returns the Milestone field.
 func (i *IssueEvent) GetMilestone() *Milestone {
 	if i == nil {
@@ -6636,6 +6652,14 @@ func (p *PublicEvent) GetSender() *User {
 	return p.Sender
 }
 
+// GetActiveLockReason returns the ActiveLockReason field if it's non-nil, zero value otherwise.
+func (p *PullRequest) GetActiveLockReason() string {
+	if p == nil || p.ActiveLockReason == nil {
+		return ""
+	}
+	return *p.ActiveLockReason
+}
+
 // GetAdditions returns the Additions field if it's non-nil, zero value otherwise.
 func (p *PullRequest) GetAdditions() int {
 	if p == nil || p.Additions == nil {
diff --git a/github/github.go b/github/github.go
index 99b928c28c1..1244e3ec1ab 100644
--- a/github/github.go
+++ b/github/github.go
@@ -111,6 +111,9 @@ const (
 	// https://developer.github.com/changes/2018-02-07-team-discussions-api/
 	mediaTypeTeamDiscussionsPreview = "application/vnd.github.echo-preview+json"
 
+	// https://developer.github.com/changes/2018-01-10-lock-reason-api-preview/
+	mediaTypeLockReasonPreview = "application/vnd.github.sailor-v-preview+json"
+
 	// https://developer.github.com/changes/2018-05-07-new-checks-api-public-beta/
 	mediaTypeCheckRunsPreview = "application/vnd.github.antiope-preview+json"
 
diff --git a/github/issues.go b/github/issues.go
index 07d6ec143e6..47537544a42 100644
--- a/github/issues.go
+++ b/github/issues.go
@@ -56,6 +56,10 @@ type Issue struct {
 	// TextMatches is only populated from search results that request text matches
 	// See: search.go and https://developer.github.com/v3/search/#text-match-metadata
 	TextMatches []TextMatch `json:"text_matches,omitempty"`
+
+	// ActiveLockReason is populated only when LockReason is provided while locking the issue.
+	// Possible values are: "off-topic", "too heated", "resolved", and "spam".
+	ActiveLockReason *string `json:"active_lock_reason,omitempty"`
 }
 
 func (i Issue) String() string {
@@ -156,7 +160,7 @@ func (s *IssuesService) listIssues(ctx context.Context, u string, opt *IssueList
 	}
 
 	// TODO: remove custom Accept headers when APIs fully launch.
-	acceptHeaders := []string{mediaTypeReactionsPreview, mediaTypeLabelDescriptionSearchPreview}
+	acceptHeaders := []string{mediaTypeReactionsPreview, mediaTypeLabelDescriptionSearchPreview, mediaTypeLockReasonPreview}
 	req.Header.Set("Accept", strings.Join(acceptHeaders, ", "))
 
 	var issues []*Issue
@@ -224,7 +228,7 @@ func (s *IssuesService) ListByRepo(ctx context.Context, owner string, repo strin
 	}
 
 	// TODO: remove custom Accept headers when APIs fully launch.
-	acceptHeaders := []string{mediaTypeReactionsPreview, mediaTypeLabelDescriptionSearchPreview}
+	acceptHeaders := []string{mediaTypeReactionsPreview, mediaTypeLabelDescriptionSearchPreview, mediaTypeLockReasonPreview}
 	req.Header.Set("Accept", strings.Join(acceptHeaders, ", "))
 
 	var issues []*Issue
@@ -247,7 +251,7 @@ func (s *IssuesService) Get(ctx context.Context, owner string, repo string, numb
 	}
 
 	// TODO: remove custom Accept headers when APIs fully launch.
-	acceptHeaders := []string{mediaTypeReactionsPreview, mediaTypeLabelDescriptionSearchPreview}
+	acceptHeaders := []string{mediaTypeReactionsPreview, mediaTypeLabelDescriptionSearchPreview, mediaTypeLockReasonPreview}
 	req.Header.Set("Accept", strings.Join(acceptHeaders, ", "))
 
 	issue := new(Issue)
@@ -303,16 +307,29 @@ func (s *IssuesService) Edit(ctx context.Context, owner string, repo string, num
 	return i, resp, nil
 }
 
+// LockIssueOptions specifies the optional parameters to the
+// IssuesService.Lock method.
+type LockIssueOptions struct {
+	// LockReason specifies the reason to lock this issue.
+	// Providing a lock reason can help make it clearer to contributors why an issue
+	// was locked. Possible values are: "off-topic", "too heated", "resolved", and "spam".
+	LockReason string `json:"lock_reason,omitempty"`
+}
+
 // Lock an issue's conversation.
 //
 // GitHub API docs: https://developer.github.com/v3/issues/#lock-an-issue
-func (s *IssuesService) Lock(ctx context.Context, owner string, repo string, number int) (*Response, error) {
+func (s *IssuesService) Lock(ctx context.Context, owner string, repo string, number int, opt *LockIssueOptions) (*Response, error) {
 	u := fmt.Sprintf("repos/%v/%v/issues/%d/lock", owner, repo, number)
-	req, err := s.client.NewRequest("PUT", u, nil)
+	req, err := s.client.NewRequest("PUT", u, opt)
 	if err != nil {
 		return nil, err
 	}
 
+	if opt != nil {
+		req.Header.Set("Accept", mediaTypeLockReasonPreview)
+	}
+
 	return s.client.Do(ctx, req, nil)
 }
 
diff --git a/github/issues_events.go b/github/issues_events.go
index 55e6d431b30..f71e46361c7 100644
--- a/github/issues_events.go
+++ b/github/issues_events.go
@@ -34,9 +34,13 @@ type IssueEvent struct {
 	//       The Actor committed to master a commit mentioning the issue in its commit message.
 	//       CommitID holds the SHA1 of the commit.
 	//
-	//     reopened, locked, unlocked
+	//     reopened, unlocked
 	//       The Actor did that to the issue.
 	//
+	//     locked
+	//       The Actor locked the issue.
+	//       LockReason holds the reason of locking the issue (if provided while locking).
+	//
 	//     renamed
 	//       The Actor changed the issue title from Rename.From to Rename.To.
 	//
@@ -64,12 +68,13 @@ type IssueEvent struct {
 	Issue     *Issue     `json:"issue,omitempty"`
 
 	// Only present on certain events; see above.
-	Assignee  *User      `json:"assignee,omitempty"`
-	Assigner  *User      `json:"assigner,omitempty"`
-	CommitID  *string    `json:"commit_id,omitempty"`
-	Milestone *Milestone `json:"milestone,omitempty"`
-	Label     *Label     `json:"label,omitempty"`
-	Rename    *Rename    `json:"rename,omitempty"`
+	Assignee   *User      `json:"assignee,omitempty"`
+	Assigner   *User      `json:"assigner,omitempty"`
+	CommitID   *string    `json:"commit_id,omitempty"`
+	Milestone  *Milestone `json:"milestone,omitempty"`
+	Label      *Label     `json:"label,omitempty"`
+	Rename     *Rename    `json:"rename,omitempty"`
+	LockReason *string    `json:"lock_reason,omitempty"`
 }
 
 // ListIssueEvents lists events for the specified issue.
@@ -87,6 +92,8 @@ func (s *IssuesService) ListIssueEvents(ctx context.Context, owner, repo string,
 		return nil, nil, err
 	}
 
+	req.Header.Set("Accept", mediaTypeLockReasonPreview)
+
 	var events []*IssueEvent
 	resp, err := s.client.Do(ctx, req, &events)
 	if err != nil {
diff --git a/github/issues_test.go b/github/issues_test.go
index e42f9750b14..d6fe9f3f919 100644
--- a/github/issues_test.go
+++ b/github/issues_test.go
@@ -20,7 +20,7 @@ func TestIssuesService_List_all(t *testing.T) {
 	client, mux, _, teardown := setup()
 	defer teardown()
 
-	acceptHeaders := []string{mediaTypeReactionsPreview, mediaTypeLabelDescriptionSearchPreview}
+	acceptHeaders := []string{mediaTypeReactionsPreview, mediaTypeLabelDescriptionSearchPreview, mediaTypeLockReasonPreview}
 	mux.HandleFunc("/issues", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "GET")
 		testHeader(t, r, "Accept", strings.Join(acceptHeaders, ", "))
@@ -57,7 +57,7 @@ func TestIssuesService_List_owned(t *testing.T) {
 	client, mux, _, teardown := setup()
 	defer teardown()
 
-	acceptHeaders := []string{mediaTypeReactionsPreview, mediaTypeLabelDescriptionSearchPreview}
+	acceptHeaders := []string{mediaTypeReactionsPreview, mediaTypeLabelDescriptionSearchPreview, mediaTypeLockReasonPreview}
 	mux.HandleFunc("/user/issues", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "GET")
 		testHeader(t, r, "Accept", strings.Join(acceptHeaders, ", "))
@@ -79,7 +79,7 @@ func TestIssuesService_ListByOrg(t *testing.T) {
 	client, mux, _, teardown := setup()
 	defer teardown()
 
-	acceptHeaders := []string{mediaTypeReactionsPreview, mediaTypeLabelDescriptionSearchPreview}
+	acceptHeaders := []string{mediaTypeReactionsPreview, mediaTypeLabelDescriptionSearchPreview, mediaTypeLockReasonPreview}
 	mux.HandleFunc("/orgs/o/issues", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "GET")
 		testHeader(t, r, "Accept", strings.Join(acceptHeaders, ", "))
@@ -109,7 +109,7 @@ func TestIssuesService_ListByRepo(t *testing.T) {
 	client, mux, _, teardown := setup()
 	defer teardown()
 
-	acceptHeaders := []string{mediaTypeReactionsPreview, mediaTypeLabelDescriptionSearchPreview}
+	acceptHeaders := []string{mediaTypeReactionsPreview, mediaTypeLabelDescriptionSearchPreview, mediaTypeLockReasonPreview}
 	mux.HandleFunc("/repos/o/r/issues", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "GET")
 		testHeader(t, r, "Accept", strings.Join(acceptHeaders, ", "))
@@ -155,7 +155,7 @@ func TestIssuesService_Get(t *testing.T) {
 	client, mux, _, teardown := setup()
 	defer teardown()
 
-	acceptHeaders := []string{mediaTypeReactionsPreview, mediaTypeLabelDescriptionSearchPreview}
+	acceptHeaders := []string{mediaTypeReactionsPreview, mediaTypeLabelDescriptionSearchPreview, mediaTypeLockReasonPreview}
 	mux.HandleFunc("/repos/o/r/issues/1", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "GET")
 		testHeader(t, r, "Accept", strings.Join(acceptHeaders, ", "))
@@ -279,7 +279,24 @@ func TestIssuesService_Lock(t *testing.T) {
 		w.WriteHeader(http.StatusNoContent)
 	})
 
-	if _, err := client.Issues.Lock(context.Background(), "o", "r", 1); err != nil {
+	if _, err := client.Issues.Lock(context.Background(), "o", "r", 1, nil); err != nil {
+		t.Errorf("Issues.Lock returned error: %v", err)
+	}
+}
+
+func TestIssuesService_LockWithReason(t *testing.T) {
+	client, mux, _, teardown := setup()
+	defer teardown()
+
+	mux.HandleFunc("/repos/o/r/issues/1/lock", func(w http.ResponseWriter, r *http.Request) {
+		testMethod(t, r, "PUT")
+		testHeader(t, r, "Accept", mediaTypeLockReasonPreview)
+		w.WriteHeader(http.StatusNoContent)
+	})
+
+	opt := &LockIssueOptions{LockReason: "off-topic"}
+
+	if _, err := client.Issues.Lock(context.Background(), "o", "r", 1, opt); err != nil {
 		t.Errorf("Issues.Lock returned error: %v", err)
 	}
 }
diff --git a/github/pulls.go b/github/pulls.go
index 78252f596af..a123ec56863 100644
--- a/github/pulls.go
+++ b/github/pulls.go
@@ -9,6 +9,7 @@ import (
 	"bytes"
 	"context"
 	"fmt"
+	"strings"
 	"time"
 )
 
@@ -61,6 +62,10 @@ type PullRequest struct {
 
 	Head *PullRequestBranch `json:"head,omitempty"`
 	Base *PullRequestBranch `json:"base,omitempty"`
+
+	// ActiveLockReason is populated only when LockReason is provided while locking the pull request.
+	// Possible values are: "off-topic", "too heated", "resolved", and "spam".
+	ActiveLockReason *string `json:"active_lock_reason,omitempty"`
 }
 
 func (p PullRequest) String() string {
@@ -118,7 +123,8 @@ func (s *PullRequestsService) List(ctx context.Context, owner string, repo strin
 	}
 
 	// TODO: remove custom Accept header when this API fully launches.
-	req.Header.Set("Accept", mediaTypeLabelDescriptionSearchPreview)
+	acceptHeaders := []string{mediaTypeLabelDescriptionSearchPreview, mediaTypeLockReasonPreview}
+	req.Header.Set("Accept", strings.Join(acceptHeaders, ", "))
 
 	var pulls []*PullRequest
 	resp, err := s.client.Do(ctx, req, &pulls)
@@ -140,7 +146,8 @@ func (s *PullRequestsService) Get(ctx context.Context, owner string, repo string
 	}
 
 	// TODO: remove custom Accept header when this API fully launches.
-	req.Header.Set("Accept", mediaTypeLabelDescriptionSearchPreview)
+	acceptHeaders := []string{mediaTypeLabelDescriptionSearchPreview, mediaTypeLockReasonPreview}
+	req.Header.Set("Accept", strings.Join(acceptHeaders, ", "))
 
 	pull := new(PullRequest)
 	resp, err := s.client.Do(ctx, req, pull)
@@ -247,7 +254,8 @@ func (s *PullRequestsService) Edit(ctx context.Context, owner string, repo strin
 	}
 
 	// TODO: remove custom Accept header when this API fully launches.
-	req.Header.Set("Accept", mediaTypeLabelDescriptionSearchPreview)
+	acceptHeaders := []string{mediaTypeLabelDescriptionSearchPreview, mediaTypeLockReasonPreview}
+	req.Header.Set("Accept", strings.Join(acceptHeaders, ", "))
 
 	p := new(PullRequest)
 	resp, err := s.client.Do(ctx, req, p)
diff --git a/github/pulls_test.go b/github/pulls_test.go
index c09d115ba31..3b2449fe0f5 100644
--- a/github/pulls_test.go
+++ b/github/pulls_test.go
@@ -20,9 +20,10 @@ func TestPullRequestsService_List(t *testing.T) {
 	client, mux, _, teardown := setup()
 	defer teardown()
 
+	acceptHeaders := []string{mediaTypeLabelDescriptionSearchPreview, mediaTypeLockReasonPreview}
 	mux.HandleFunc("/repos/o/r/pulls", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "GET")
-		testHeader(t, r, "Accept", mediaTypeLabelDescriptionSearchPreview)
+		testHeader(t, r, "Accept", strings.Join(acceptHeaders, ", "))
 		testFormValues(t, r, values{
 			"state":     "closed",
 			"head":      "h",
@@ -58,9 +59,10 @@ func TestPullRequestsService_Get(t *testing.T) {
 	client, mux, _, teardown := setup()
 	defer teardown()
 
+	acceptHeaders := []string{mediaTypeLabelDescriptionSearchPreview, mediaTypeLockReasonPreview}
 	mux.HandleFunc("/repos/o/r/pulls/1", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "GET")
-		testHeader(t, r, "Accept", mediaTypeLabelDescriptionSearchPreview)
+		testHeader(t, r, "Accept", strings.Join(acceptHeaders, ", "))
 		fmt.Fprint(w, `{"number":1}`)
 	})
 
@@ -278,9 +280,10 @@ func TestPullRequestsService_Edit(t *testing.T) {
 
 	for i, tt := range tests {
 		madeRequest := false
+		acceptHeaders := []string{mediaTypeLabelDescriptionSearchPreview, mediaTypeLockReasonPreview}
 		mux.HandleFunc(fmt.Sprintf("/repos/o/r/pulls/%v", i), func(w http.ResponseWriter, r *http.Request) {
 			testMethod(t, r, "PATCH")
-			testHeader(t, r, "Accept", mediaTypeLabelDescriptionSearchPreview)
+			testHeader(t, r, "Accept", strings.Join(acceptHeaders, ", "))
 			testBody(t, r, tt.wantUpdate+"\n")
 			io.WriteString(w, tt.sendResponse)
 			madeRequest = true