diff --git a/party b/party
index a464a01..a21c1fd 100755
--- a/party
+++ b/party
@@ -387,6 +387,15 @@ apply_party_perms_file() {
 # directory.
 validate_socket_dir_parent() {
     p="$PARTY_SOCKET_DIR"
+    # Whitespace in the parent breaks every `for rec in $(roster_list)`
+    # walker and the unquoted paths embedded in tmux hook/status-right
+    # strings. Refuse at host time, where the dir is chosen, instead of
+    # corrupting quietly later.
+    case "$p" in
+        *[[:space:]]*)
+            echo "party: PARTY_SOCKET_DIR must not contain whitespace: $p" >&2
+            return 1 ;;
+    esac
     if [ ! -d "$p" ]; then
         echo "party: PARTY_SOCKET_DIR $p does not exist" >&2
         return 1
@@ -530,6 +539,12 @@ pick_live_party() {
         0) echo "party: no parties found on this host." >&2; return 1 ;;
         1) roster_read "$1"; return 0 ;;
     esac
+    # 2+ parties need the interactive picker; without a tty read would
+    # EOF and set -e would kill us with no message.
+    if [ ! -t 0 ]; then
+        echo "party: multiple parties running; pass a name (see 'party list')." >&2
+        return 1
+    fi
     i=0
     for r in "$@"; do
         i=$((i+1))
diff --git a/tests/20-helpers.bats b/tests/20-helpers.bats
index 805c7be..8f37501 100644
--- a/tests/20-helpers.bats
+++ b/tests/20-helpers.bats
@@ -109,3 +109,30 @@ setup() {
   # to also confirm a foreign-uid PID is not preventing the result.
   ! is_party_alive 1 "$PARTY_TMP/no-such-sock"
 }
+
+@test "validate_socket_dir_parent refuses whitespace in PARTY_SOCKET_DIR" {
+  spaced="$PARTY_TMP/with space"
+  mkdir -p "$spaced"
+  chmod 0700 "$spaced"
+  PARTY_SOCKET_DIR="$spaced" run validate_socket_dir_parent
+  [ "$status" -ne 0 ]
+  [[ "$output" == *"whitespace"* ]]
+}
+
+@test "pick_live_party without a tty fails with guidance, not a silent death" {
+  # Two live-looking parties force the numbered picker; stdin is not a
+  # tty under bats, so the guard must fire before read.
+  stub="$PARTY_TMP/tmux-ok"
+  printf '#!/bin/sh\nexit 0\n' > "$stub"
+  chmod +x "$stub"
+  export PARTY_TMUX="$stub"
+  ensure_party_dir "$USER" one
+  ensure_party_dir "$USER" two
+  for n in one two; do
+    d="$PARTY_SOCKET_DIR/party-$USER:$n.d"
+    printf 'SERVER_PID=1\nGROUP=%s\n' "$(id -gn)" > "$d/roster"
+  done
+  run pick_live_party
+  [ "$status" -ne 0 ]
+  [[ "$output" == *"pass a name"* ]]
+}