diff --git a/cmd/auth/login.go b/cmd/auth/login.go
index 365b495ba..916fda9ea 100644
--- a/cmd/auth/login.go
+++ b/cmd/auth/login.go
@@ -62,7 +62,7 @@ browser. Run it in the background and retrieve the verification URL from its out
 	}
 	cmdutil.SetSupportedIdentities(cmd, []string{"user"})
 
-	cmd.Flags().StringVar(&opts.Scope, "scope", "", "scopes to request (space-separated)")
+	cmd.Flags().StringVar(&opts.Scope, "scope", "", "scopes to request (space- or comma-separated)")
 	cmd.Flags().BoolVar(&opts.Recommend, "recommend", false, "request only recommended (auto-approve) scopes")
 	available := sortedKnownDomains()
 	cmd.Flags().StringSliceVar(&opts.Domains, "domain", nil,
@@ -185,7 +185,11 @@ func authLoginRun(opts *LoginOptions) error {
 		}
 	}
 
-	finalScope := opts.Scope
+	// Normalize --scope so users can pass either OAuth-standard space-separated
+	// values or the more natural comma-separated list. RFC 6749 §3.3 mandates
+	// space-delimited scopes in the wire request, so the device authorization
+	// endpoint rejects raw "a,b" strings as a single malformed scope.
+	finalScope := normalizeScopeInput(opts.Scope)
 
 	// Resolve scopes from domain/permission filters
 	if len(selectedDomains) > 0 || opts.Recommend {
@@ -532,6 +536,40 @@ func shortcutSupportsIdentity(sc common.Shortcut, identity string) bool {
 	return false
 }
 
+// normalizeScopeInput accepts a user-supplied --scope value that may use
+// commas, spaces, tabs, or newlines (or any mix) as separators and returns the
+// canonical OAuth 2.0 wire form: a single space-joined string with empties
+// trimmed and duplicates removed (first occurrence wins; order preserved).
+//
+// Examples:
+//
+//	"vc:note:read,vc:meeting.meetingevent:read" -> "vc:note:read vc:meeting.meetingevent:read"
+//	"a, b ,  c"                                 -> "a b c"
+//	"a b a"                                     -> "a b"
+//	""                                          -> ""
+func normalizeScopeInput(raw string) string {
+	if raw == "" {
+		return ""
+	}
+	// Treat both commas and any whitespace as separators.
+	fields := strings.FieldsFunc(raw, func(r rune) bool {
+		return r == ',' || r == ' ' || r == '\t' || r == '\n' || r == '\r'
+	})
+	if len(fields) == 0 {
+		return ""
+	}
+	seen := make(map[string]struct{}, len(fields))
+	out := make([]string, 0, len(fields))
+	for _, f := range fields {
+		if _, ok := seen[f]; ok {
+			continue
+		}
+		seen[f] = struct{}{}
+		out = append(out, f)
+	}
+	return strings.Join(out, " ")
+}
+
 // suggestDomain finds the best "did you mean" match for an unknown domain.
 func suggestDomain(input string, known map[string]bool) string {
 	// Check common cases: prefix match or input is a substring
diff --git a/cmd/auth/login_test.go b/cmd/auth/login_test.go
index ea9503464..8687d313a 100644
--- a/cmd/auth/login_test.go
+++ b/cmd/auth/login_test.go
@@ -70,6 +70,32 @@ func TestSuggestDomain_ExactMatch(t *testing.T) {
 	}
 }
 
+func TestNormalizeScopeInput(t *testing.T) {
+	cases := []struct {
+		name string
+		in   string
+		want string
+	}{
+		{"empty", "", ""},
+		{"single", "vc:note:read", "vc:note:read"},
+		{"comma", "vc:note:read,vc:meeting.meetingevent:read", "vc:note:read vc:meeting.meetingevent:read"},
+		{"space", "vc:note:read vc:meeting.meetingevent:read", "vc:note:read vc:meeting.meetingevent:read"},
+		{"comma_and_spaces", "vc:note:read, vc:meeting.meetingevent:read", "vc:note:read vc:meeting.meetingevent:read"},
+		{"mixed_separators", "a, b\tc\nd  e", "a b c d e"},
+		{"trim_and_dedup", "  a , b , a  ", "a b"},
+		{"trailing_separators", "a,b,,", "a b"},
+		{"only_separators", " , , ", ""},
+		{"tab_separated", "im:message:send\toffline_access", "im:message:send offline_access"},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := normalizeScopeInput(tc.in); got != tc.want {
+				t.Errorf("normalizeScopeInput(%q) = %q, want %q", tc.in, got, tc.want)
+			}
+		})
+	}
+}
+
 func TestShortcutSupportsIdentity_DefaultUser(t *testing.T) {
 	// Empty AuthTypes defaults to ["user"]
 	sc := common.Shortcut{AuthTypes: nil}