diff --git a/github/repos.go b/github/repos.go
index a57b260e95a..6631c6745d0 100644
--- a/github/repos.go
+++ b/github/repos.go
@@ -249,7 +249,7 @@ func (s *RepositoriesService) ListByOrg(ctx context.Context, org string, opts *R
 
 	// TODO: remove custom Accept headers when APIs fully launch.
 	acceptHeaders := []string{mediaTypeTopicsPreview}
-	req.Header.Set("Accept", strings.Join(acceptHeaders, ", "))
+	req.Header.Set("Accept:", strings.Join(acceptHeaders, ", "))
 
 	var repos []*Repository
 	resp, err := s.client.Do(ctx, req, &repos)
@@ -368,7 +368,7 @@ func (s *RepositoriesService) Create(ctx context.Context, org string, repo *Repo
 	}
 
 	acceptHeaders := []string{mediaTypeRepositoryTemplatePreview, mediaTypeRepositoryVisibilityPreview}
-	req.Header.Set("Accept", strings.Join(acceptHeaders, ", "))
+	req.Header.Set("Accept:", strings.Join(acceptHeaders, ", "))
 	r := new(Repository)
 	resp, err := s.client.Do(ctx, req, r)
 	if err != nil {
@@ -427,7 +427,7 @@ func (s *RepositoriesService) Get(ctx context.Context, owner, repo string) (*Rep
 		mediaTypeRepositoryTemplatePreview,
 		mediaTypeRepositoryVisibilityPreview,
 	}
-	req.Header.Set("Accept", strings.Join(acceptHeaders, ", "))
+	req.Header.Set("Accept:", strings.Join(acceptHeaders, ", "))
 
 	repository := new(Repository)
 	resp, err := s.client.Do(ctx, req, repository)
@@ -490,7 +490,7 @@ func (s *RepositoriesService) Edit(ctx context.Context, owner, repo string, repo
 	}
 
 	acceptHeaders := []string{mediaTypeRepositoryTemplatePreview, mediaTypeRepositoryVisibilityPreview}
-	req.Header.Set("Accept", strings.Join(acceptHeaders, ", "))
+	req.Header.Set("Accept:", strings.Join(acceptHeaders, ", "))
 	r := new(Repository)
 	resp, err := s.client.Do(ctx, req, r)
 	if err != nil {
@@ -1308,7 +1308,7 @@ func (s *RepositoriesService) ListAllTopics(ctx context.Context, owner, repo str
 	}
 
 	// TODO: remove custom Accept header when this API fully launches.
-	req.Header.Set("Accept", mediaTypeTopicsPreview)
+	req.Header.Set("Accept:", mediaTypeTopicsPreview)
 
 	topics := new(repositoryTopics)
 	resp, err := s.client.Do(ctx, req, topics)
@@ -1336,7 +1336,7 @@ func (s *RepositoriesService) ReplaceAllTopics(ctx context.Context, owner, repo
 	}
 
 	// TODO: remove custom Accept header when this API fully launches.
-	req.Header.Set("Accept", mediaTypeTopicsPreview)
+	req.Header.Set("Accept:", mediaTypeTopicsPreview)
 
 	t = new(repositoryTopics)
 	resp, err := s.client.Do(ctx, req, t)
diff --git a/github/repos_test.go b/github/repos_test.go
index bbe82ea6a75..0acbce00aae 100644
--- a/github/repos_test.go
+++ b/github/repos_test.go
@@ -22,7 +22,7 @@ func TestRepositoriesService_List_authenticatedUser(t *testing.T) {
 	wantAcceptHeaders := []string{mediaTypeTopicsPreview, mediaTypeRepositoryVisibilityPreview}
 	mux.HandleFunc("/user/repos", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "GET")
-		testHeader(t, r, "Accept", strings.Join(wantAcceptHeaders, ", "))
+		testHeader(t, r, "Accept:", strings.Join(wantAcceptHeaders, ", "))
 		fmt.Fprint(w, `[{"id":1},{"id":2}]`)
 	})
 
@@ -59,7 +59,7 @@ func TestRepositoriesService_List_specifiedUser(t *testing.T) {
 	wantAcceptHeaders := []string{mediaTypeTopicsPreview, mediaTypeRepositoryVisibilityPreview}
 	mux.HandleFunc("/users/u/repos", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "GET")
-		testHeader(t, r, "Accept", strings.Join(wantAcceptHeaders, ", "))
+		testHeader(t, r, "Accept:", strings.Join(wantAcceptHeaders, ", "))
 		testFormValues(t, r, values{
 			"visibility":  "public",
 			"affiliation": "owner,collaborator",
@@ -96,7 +96,7 @@ func TestRepositoriesService_List_specifiedUser_type(t *testing.T) {
 	wantAcceptHeaders := []string{mediaTypeTopicsPreview, mediaTypeRepositoryVisibilityPreview}
 	mux.HandleFunc("/users/u/repos", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "GET")
-		testHeader(t, r, "Accept", strings.Join(wantAcceptHeaders, ", "))
+		testHeader(t, r, "Accept:", strings.Join(wantAcceptHeaders, ", "))
 		testFormValues(t, r, values{
 			"type": "owner",
 		})
@@ -230,7 +230,7 @@ func TestRepositoriesService_Create_user(t *testing.T) {
 		json.NewDecoder(r.Body).Decode(v)
 
 		testMethod(t, r, "POST")
-		testHeader(t, r, "Accept", strings.Join(wantAcceptHeaders, ", "))
+		testHeader(t, r, "Accept:", strings.Join(wantAcceptHeaders, ", "))
 		want := &createRepoRequest{Name: String("n")}
 		if !reflect.DeepEqual(v, want) {
 			t.Errorf("Request body = %+v, want %+v", v, want)
@@ -280,7 +280,7 @@ func TestRepositoriesService_Create_org(t *testing.T) {
 		json.NewDecoder(r.Body).Decode(v)
 
 		testMethod(t, r, "POST")
-		testHeader(t, r, "Accept", strings.Join(wantAcceptHeaders, ", "))
+		testHeader(t, r, "Accept:", strings.Join(wantAcceptHeaders, ", "))
 		want := &createRepoRequest{Name: String("n")}
 		if !reflect.DeepEqual(v, want) {
 			t.Errorf("Request body = %+v, want %+v", v, want)
@@ -356,7 +356,7 @@ func TestRepositoriesService_Get(t *testing.T) {
 	wantAcceptHeaders := []string{mediaTypeCodesOfConductPreview, mediaTypeTopicsPreview, mediaTypeRepositoryTemplatePreview, mediaTypeRepositoryVisibilityPreview}
 	mux.HandleFunc("/repos/o/r", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "GET")
-		testHeader(t, r, "Accept", strings.Join(wantAcceptHeaders, ", "))
+		testHeader(t, r, "Accept:", strings.Join(wantAcceptHeaders, ", "))
 		fmt.Fprint(w, `{"id":1,"name":"n","description":"d","owner":{"login":"l"},"license":{"key":"mit"}}`)
 	})
 
@@ -476,7 +476,7 @@ func TestRepositoriesService_Edit(t *testing.T) {
 		json.NewDecoder(r.Body).Decode(v)
 
 		testMethod(t, r, "PATCH")
-		testHeader(t, r, "Accept", strings.Join(wantAcceptHeaders, ", "))
+		testHeader(t, r, "Accept:", strings.Join(wantAcceptHeaders, ", "))
 		if !reflect.DeepEqual(v, input) {
 			t.Errorf("Request body = %+v, want %+v", v, input)
 		}
@@ -1893,7 +1893,7 @@ func TestRepositoriesService_ListAllTopics(t *testing.T) {
 
 	mux.HandleFunc("/repos/o/r/topics", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "GET")
-		testHeader(t, r, "Accept", mediaTypeTopicsPreview)
+		testHeader(t, r, "Accept:", mediaTypeTopicsPreview)
 		fmt.Fprint(w, `{"names":["go", "go-github", "github"]}`)
 	})
 
@@ -1929,7 +1929,7 @@ func TestRepositoriesService_ListAllTopics_emptyTopics(t *testing.T) {
 
 	mux.HandleFunc("/repos/o/r/topics", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "GET")
-		testHeader(t, r, "Accept", mediaTypeTopicsPreview)
+		testHeader(t, r, "Accept:", mediaTypeTopicsPreview)
 		fmt.Fprint(w, `{"names":[]}`)
 	})
 
@@ -1951,7 +1951,7 @@ func TestRepositoriesService_ReplaceAllTopics(t *testing.T) {
 
 	mux.HandleFunc("/repos/o/r/topics", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "PUT")
-		testHeader(t, r, "Accept", mediaTypeTopicsPreview)
+		testHeader(t, r, "Accept:", mediaTypeTopicsPreview)
 		fmt.Fprint(w, `{"names":["go", "go-github", "github"]}`)
 	})
 
@@ -1987,7 +1987,7 @@ func TestRepositoriesService_ReplaceAllTopics_nilSlice(t *testing.T) {
 
 	mux.HandleFunc("/repos/o/r/topics", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "PUT")
-		testHeader(t, r, "Accept", mediaTypeTopicsPreview)
+		testHeader(t, r, "Accept:", mediaTypeTopicsPreview)
 		testBody(t, r, `{"names":[]}`+"\n")
 		fmt.Fprint(w, `{"names":[]}`)
 	})
@@ -2010,7 +2010,7 @@ func TestRepositoriesService_ReplaceAllTopics_emptySlice(t *testing.T) {
 
 	mux.HandleFunc("/repos/o/r/topics", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "PUT")
-		testHeader(t, r, "Accept", mediaTypeTopicsPreview)
+		testHeader(t, r, "Accept:", mediaTypeTopicsPreview)
 		testBody(t, r, `{"names":[]}`+"\n")
 		fmt.Fprint(w, `{"names":[]}`)
 	})