diff --git a/vm/cocoon_cli.go b/vm/cocoon_cli.go
index 0786176..82ccf43 100644
--- a/vm/cocoon_cli.go
+++ b/vm/cocoon_cli.go
@@ -180,8 +180,10 @@ func (c *CocoonCLI) Exec(ctx context.Context, vmID string, argv []string, env ma
 	if len(argv) == 0 {
 		return errors.New("cocoon vm exec: argv is empty")
 	}
-	cmd := c.command(ctx, buildExecArgs(vmID, argv, env)...)
-	cmd.Stdin = stdin
+	cmd := c.command(ctx, buildExecArgs(vmID, argv, env, stdin != nil)...)
+	if stdin != nil {
+		cmd.Stdin = stdin
+	}
 	cmd.Stdout = stdout
 	cmd.Stderr = stderr
 	if err := cmd.Run(); err != nil {
@@ -464,12 +466,14 @@ func buildRunArgs(opts RunOptions) []string {
 	return args
 }
 
-// buildExecArgs assembles `cocoon vm exec [-e KEY=VAL...] <vmID> -- <argv>...`.
-// Env keys are sorted so the resulting argv is deterministic (test-friendly,
-// log-friendly); cocoon doesn't care about order.
-func buildExecArgs(vmID string, argv []string, env map[string]string) []string {
-	args := make([]string, 0, 4+2*len(env)+len(argv)) //nolint:mnd
+// buildExecArgs assembles `cocoon vm exec [-i] [-e KEY=VAL...] <vmID> -- <argv>...`,
+// sorting env keys for a deterministic argv. -i attaches stdin (opt-in, docker semantics).
+func buildExecArgs(vmID string, argv []string, env map[string]string, interactive bool) []string {
+	args := make([]string, 0, 5+2*len(env)+len(argv)) //nolint:mnd
 	args = append(args, "vm", "exec")
+	if interactive {
+		args = append(args, "-i")
+	}
 	for _, k := range slices.Sorted(maps.Keys(env)) {
 		args = append(args, "-e", k+"="+env[k])
 	}
diff --git a/vm/cocoon_cli_test.go b/vm/cocoon_cli_test.go
index f48e56e..392e450 100644
--- a/vm/cocoon_cli_test.go
+++ b/vm/cocoon_cli_test.go
@@ -214,11 +214,12 @@ func TestBuildExecArgsAssemblesEnvAndArgv(t *testing.T) {
 	t.Parallel()
 
 	cases := []struct {
-		name string
-		vmID string
-		argv []string
-		env  map[string]string
-		want []string
+		name        string
+		vmID        string
+		argv        []string
+		env         map[string]string
+		interactive bool
+		want        []string
 	}{
 		{
 			name: "no env passes through plain argv",
@@ -239,10 +240,18 @@ func TestBuildExecArgsAssemblesEnvAndArgv(t *testing.T) {
 			argv: []string{"--", "ls"},
 			want: []string{"vm", "exec", "vm-3", "--", "--", "ls"},
 		},
+		{
+			name:        "interactive adds -i before env",
+			vmID:        "vm-4",
+			argv:        []string{"cat"},
+			env:         map[string]string{"FOO": "1"},
+			interactive: true,
+			want:        []string{"vm", "exec", "-i", "-e", "FOO=1", "vm-4", "--", "cat"},
+		},
 	}
 	for _, tc := range cases {
 		t.Run(tc.name, func(t *testing.T) {
-			got := buildExecArgs(tc.vmID, tc.argv, tc.env)
+			got := buildExecArgs(tc.vmID, tc.argv, tc.env, tc.interactive)
 			if !reflect.DeepEqual(got, tc.want) {
 				t.Fatalf("buildExecArgs() = %#v, want %#v", got, tc.want)
 			}