diff --git a/README.md b/README.md
index 4903928..57b39bd 100644
--- a/README.md
+++ b/README.md
@@ -6,7 +6,7 @@ identities and child mnemonics, each of which can be recreated from that
 mnemonic at any time. The same mnemonic, key type and index always give the same
 key.
 
-It uses the BIP-85 entropy deriver from `git.eeqj.de/sneak/secret/pkg/bip85` and
+It uses the BIP-85 entropy deriver from `sneak.berlin/go/secret/pkg/bip85` and
 takes the same steps as that repository's `agehd` package.
 
 Commands are grouped by what is derived: `keyfunc ssh ...` for ed25519 SSH keys,
@@ -100,7 +100,9 @@ m/83696968'/<app>'/<n>'
   to one tool. Each key type's number is spelled the way BIP-85 spells its own
   RSA application (`828365` is the ASCII codes of `R`, `S`, `A` written out):
   SSH is `838372` (`S` `S` `H`), age is `657169` (`A` `G` `E`).
-- `n` is the key index: flag `--index` / `-n`, default `0`.
+- `n` is the key index, a decimal number: flag `--index` / `-n`, default `0`. A
+  leading zero is still decimal (`-n 010` is index 10); a base prefix, an
+  underscore or a sign (`0x10`, `1_0`, `+1`) is refused.
 
 ## Giving it the mnemonic
 
diff --git a/go.mod b/go.mod
index 107494e..8a4b92a 100644
--- a/go.mod
+++ b/go.mod
@@ -4,13 +4,13 @@ go 1.26.0
 
 require (
 	filippo.io/age v1.3.2
-	git.eeqj.de/sneak/secret v0.0.0-20260810132333-41cea400a7fd
 	github.com/btcsuite/btcd v0.25.0
 	github.com/btcsuite/btcd/btcutil v1.2.0
 	github.com/spf13/cobra v1.10.2
 	github.com/stretchr/testify v1.12.1
 	golang.org/x/crypto v0.57.0
 	golang.org/x/term v0.46.0
+	sneak.berlin/go/secret v0.0.0-20261007105610-ef0ae90768c8
 )
 
 require (
diff --git a/go.sum b/go.sum
index 5c2cbff..a6b1fa6 100644
--- a/go.sum
+++ b/go.sum
@@ -4,8 +4,6 @@ filippo.io/age v1.3.2 h1:r6RSZLFSMm6rzKepZ7ZAYkKCu14f3/Me8c7uKYh7C8c=
 filippo.io/age v1.3.2/go.mod h1:TH/Yr2sSRhCKbaH4XPxpUV0Us8Gv6txYUpiZQWz8Evk=
 filippo.io/hpke v0.4.0 h1:p575VVQ6ted4pL+it6M00V/f2qTZITO0zgmdKCkd5+A=
 filippo.io/hpke v0.4.0/go.mod h1:EmAN849/P3qdeK+PCMkDpDm83vRHM5cDipBJ8xbQLVY=
-git.eeqj.de/sneak/secret v0.0.0-20260810132333-41cea400a7fd h1:6YFV6horz2wDFPWWhour8qx8gLGyO0qoplwEeOuQ2J4=
-git.eeqj.de/sneak/secret v0.0.0-20260810132333-41cea400a7fd/go.mod h1:gKCcMZvlBOqusn/BxR8IyFmSJQr6R4vvjJ926iNpOSI=
 github.com/btcsuite/btcd v0.25.0 h1:JPbjwvHGpSywBRuorFFqTjaVP4y6Qw69XJ1nQ6MyWJM=
 github.com/btcsuite/btcd v0.25.0/go.mod h1:qbPE+pEiR9643E1s1xu57awsRhlCIm1ZIi6FfeRA4KE=
 github.com/btcsuite/btcd/btcec/v2 v2.5.0 h1:KioMXOWa76b86sTZZOmbzv/ldaQCmB8KFAyn5PbB8E8=
@@ -30,8 +28,6 @@ github.com/spf13/pflag v1.0.9 h1:9exaQaMOCwffKiiiYk6/BndUBv+iRViNW+4lEMi0PvY=
 github.com/spf13/pflag v1.0.9/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
 github.com/stretchr/testify v1.12.1 h1:EuwCh5fleGS7H32xRwO3wRGT7DxrDhLAT6FF8MpWDWE=
 github.com/stretchr/testify v1.12.1/go.mod h1:MDEgiDPPsNp5cuIrHPPCyornHKgEVbtFUmoNlxoYthg=
-github.com/tyler-smith/go-bip39 v1.1.0 h1:5eUemwrMargf3BSLRRCalXT93Ns6pQJIjYQN2nyfOP8=
-github.com/tyler-smith/go-bip39 v1.1.0/go.mod h1:gUYDtqQw1JS3ZJ8UWVcGTGqqr6YIN3CWg+kkNaLt55U=
 go.yaml.in/yaml/v3 v3.0.4/go.mod h1:DhzuOOF2ATzADvBadXxruRBLzYTpT36CKvDb3+aBEFg=
 go.yaml.in/yaml/v3 v3.0.5 h1:N6y/pJk8buWs9NY5ERU2HSMfm+IuD/OtfdAnq6kESPw=
 go.yaml.in/yaml/v3 v3.0.5/go.mod h1:HVTZu1O7/Vkt2N+BFy8Zza+lnLsABggaTM2ZpNIGuKg=
@@ -42,3 +38,5 @@ golang.org/x/sys v0.48.0/go.mod h1:hNLxWAXmnKAxqDtdwIYC4bM9oQPEecfsnNMuSxOs3og=
 golang.org/x/term v0.46.0 h1:3+OXuTbaKDgwk8jTi3aSLHRlmWqHEUDUtxnbFigO4YE=
 golang.org/x/term v0.46.0/go.mod h1:+K02xbkittuwc0Am4abfA3Fc+XRGXkvBXNO88NCXPoc=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+sneak.berlin/go/secret v0.0.0-20261007105610-ef0ae90768c8 h1:Bd2bUsRCN8xhcrpH3LpJqHxR2QffeOuF5z76iP4BFnw=
+sneak.berlin/go/secret v0.0.0-20261007105610-ef0ae90768c8/go.mod h1:uVx9ZuE7ZMIOBY2B1ElXCs97CTsEfuham3NQRdLj5lI=
diff --git a/internal/childmnemonic/childmnemonic.go b/internal/childmnemonic/childmnemonic.go
index c4d6b89..7b6c7d0 100644
--- a/internal/childmnemonic/childmnemonic.go
+++ b/internal/childmnemonic/childmnemonic.go
@@ -5,10 +5,10 @@ import (
 	"errors"
 	"fmt"
 
-	"git.eeqj.de/sneak/secret/pkg/bip85"
 	"github.com/btcsuite/btcd/btcutil/hdkeychain"
 	"sneak.berlin/go/keyfunc/internal/bip39"
 	"sneak.berlin/go/keyfunc/internal/derive"
+	"sneak.berlin/go/secret/pkg/bip85"
 )
 
 // english is the number BIP-85 gives the English word list.
diff --git a/internal/cli/cli_test.go b/internal/cli/cli_test.go
index 0b29adc..8113091 100644
--- a/internal/cli/cli_test.go
+++ b/internal/cli/cli_test.go
@@ -2,6 +2,7 @@ package cli_test
 
 import (
 	"bytes"
+	"strconv"
 	"strings"
 	"testing"
 
@@ -106,6 +107,56 @@ func TestAnIndexWithNoHardenedChildIsRefused(t *testing.T) {
 	require.Empty(t, out)
 }
 
+func TestAnIndexWithALeadingZeroIsDecimal(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	line := run(t, "ssh", "pub", "-n", "010")
+	require.Equal(t, run(t, "ssh", "pub", "-n", "10"), line)
+	require.True(t,
+		strings.HasSuffix(strings.TrimSpace(line), " keyfunc/ssh/10"),
+	)
+}
+
+// The mnemonic command in these runs fails, so a refusal naming the
+// flag shows that the number was refused before the mnemonic was
+// looked for.
+func TestAnIndexThatIsNotDecimalDigitsIsRefused(t *testing.T) {
+	t.Parallel()
+
+	for _, index := range []string{"0x10", "1_0", "+1", "-1", ""} {
+		t.Run(index, func(t *testing.T) {
+			t.Parallel()
+
+			out, err := execute(t,
+				"ssh", "pub", "-n", index, "--mnemonic-command", "exit 1",
+			)
+			require.ErrorIs(t, err, strconv.ErrSyntax)
+			require.ErrorContains(t, err, "--index")
+			require.Empty(t, out)
+		})
+	}
+}
+
+// Neither a command group nor --version reads the index, so these
+// show that it is refused while the flags are parsed.
+func TestAnIndexNotInDecimalIsRefusedBeforeAnyCommandRuns(t *testing.T) {
+	t.Parallel()
+
+	for _, args := range [][]string{
+		{"ssh", "-n", "0x10"},
+		{"-n", "0x10", "--version"},
+	} {
+		t.Run(strings.Join(args, " "), func(t *testing.T) {
+			t.Parallel()
+
+			out, err := execute(t, args...)
+			require.ErrorIs(t, err, strconv.ErrSyntax)
+			require.ErrorContains(t, err, "--index")
+			require.Empty(t, out)
+		})
+	}
+}
+
 func TestTheMnemonicCommandIsUsed(t *testing.T) {
 	t.Setenv(mnemonic.Variable, "")
 
@@ -138,6 +189,22 @@ func TestALengthTheToolDoesNotOfferIsRefused(t *testing.T) {
 	require.Empty(t, out)
 }
 
+func TestTheWordCountIsDecimal(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	words := strings.Fields(run(t, "mnemonic", "--words", "012"))
+	require.Len(t, words, twelve)
+
+	// As for the index, the failing mnemonic command shows that the
+	// number was refused first.
+	out, err := execute(t,
+		"mnemonic", "--words", "0x18", "--mnemonic-command", "exit 1",
+	)
+	require.ErrorIs(t, err, strconv.ErrSyntax)
+	require.ErrorContains(t, err, "--words")
+	require.Empty(t, out)
+}
+
 // run executes the tool with the given arguments and returns what it
 // wrote to standard output.
 func run(t *testing.T, args ...string) string {
diff --git a/internal/cli/mnemonic/mnemonic.go b/internal/cli/mnemonic/mnemonic.go
index 8c33332..05fdcea 100644
--- a/internal/cli/mnemonic/mnemonic.go
+++ b/internal/cli/mnemonic/mnemonic.go
@@ -31,8 +31,9 @@ func Command() *cobra.Command {
 		},
 	}
 
-	cmd.Flags().Uint32(
-		"words", childmnemonic.DefaultWords,
+	words := options.Decimal(childmnemonic.DefaultWords)
+	cmd.Flags().Var(
+		&words, "words",
 		"how long the child mnemonic is: 12, 18 or 24 words",
 	)
 
diff --git a/internal/cli/options/options.go b/internal/cli/options/options.go
index 5d454ec..c008541 100644
--- a/internal/cli/options/options.go
+++ b/internal/cli/options/options.go
@@ -4,6 +4,7 @@ package options
 
 import (
 	"fmt"
+	"strconv"
 
 	"github.com/spf13/cobra"
 	"sneak.berlin/go/keyfunc/internal/mnemonic"
@@ -16,8 +17,8 @@ func Add(cmd *cobra.Command) {
 		"mnemonic-command", "",
 		"shell command whose output is the mnemonic",
 	)
-	cmd.PersistentFlags().Uint32P(
-		"index", "n", 0,
+	cmd.PersistentFlags().VarP(
+		new(Decimal), "index", "n",
 		"which key to derive",
 	)
 }
@@ -41,3 +42,33 @@ func Mnemonic(cmd *cobra.Command) (string, error) {
 
 	return mnemonic.Read(cmd.Context(), command)
 }
+
+// Decimal is a flag value for a number written in decimal digits only.
+// The flag library's own uint32 flags read 010 as octal 8 and also
+// take 0x10 or 1_0.
+type Decimal uint32
+
+// String returns the number in decimal digits.
+func (d *Decimal) String() string {
+	return strconv.FormatUint(uint64(*d), 10)
+}
+
+// Set reads text as a decimal number that fits in 32 bits: a leading
+// zero is still decimal, and a base prefix, an underscore or a sign is
+// refused.
+func (d *Decimal) Set(text string) error {
+	number, err := strconv.ParseUint(text, 10, 32)
+	if err != nil {
+		return err
+	}
+
+	*d = Decimal(number)
+
+	return nil
+}
+
+// Type is what --help shows as the flag's type, and what GetUint32
+// checks before it reads the value back.
+func (d *Decimal) Type() string {
+	return "uint32"
+}
diff --git a/internal/derive/derive.go b/internal/derive/derive.go
index cc98fa3..55b944b 100644
--- a/internal/derive/derive.go
+++ b/internal/derive/derive.go
@@ -5,10 +5,10 @@ import (
 	"errors"
 	"fmt"
 
-	"git.eeqj.de/sneak/secret/pkg/bip85"
 	"github.com/btcsuite/btcd/btcutil/hdkeychain"
 	"github.com/btcsuite/btcd/chaincfg"
 	"sneak.berlin/go/keyfunc/internal/bip39"
+	"sneak.berlin/go/secret/pkg/bip85"
 )
 
 const (