diff --git a/install.sh b/install.sh
index 6d6070a..0336b72 100755
--- a/install.sh
+++ b/install.sh
@@ -118,17 +118,31 @@ read -rp "Type 'yes' to proceed: " confirm
 
 # === Shrink Windows ===
 # Convert NIXOS_SIZE (e.g. "200G") to bytes for ntfsresize
-case "$NIXOS_SIZE" in
-  *G|*g) nixos_bytes=$(( ${NIXOS_SIZE%[Gg]} * 1024 * 1024 * 1024 )) ;;
-  *M|*m) nixos_bytes=$(( ${NIXOS_SIZE%[Mm]} * 1024 * 1024 )) ;;
-  *)     nixos_bytes="$NIXOS_SIZE" ;;
-esac
-log "Shrinking Windows partition by $NIXOS_SIZE ($nixos_bytes bytes) — this may take a few minutes..."
+size_to_bytes() {
+  local s="$1"
+  case "$s" in
+    *G|*g) echo $(( ${s%[Gg]} * 1024 * 1024 * 1024 )) ;;
+    *M|*m) echo $(( ${s%[Mm]} * 1024 * 1024 )) ;;
+    *K|*k) echo $(( ${s%[Kk]} * 1024 )) ;;
+    *)     echo "$s" ;;
+  esac
+}
+nixos_bytes=$(size_to_bytes "$NIXOS_SIZE")
+# Same for SWAP_SIZE so we can shrink the Windows partition by the *total* of
+# both new partitions (NixOS root + swap). Without this, the swap partition
+# would never fit on disk.
+if [[ "$SWAP_SIZE" == "0" ]]; then
+  shrink_bytes=$nixos_bytes
+else
+  swap_bytes=$(size_to_bytes "$SWAP_SIZE")
+  shrink_bytes=$(( nixos_bytes + swap_bytes ))
+fi
+log "Shrinking Windows partition by $NIXOS_SIZE (nixos) ${SWAP_SIZE:+ + $SWAP_SIZE (swap)} ($shrink_bytes bytes total) — this may take a few minutes..."
 ntfsfix -d "$WIN_PART" 2>/dev/null || true
 # ntfsresize syntax: -s = perform the shrink, --size = new size in bytes
-# We want the new Windows partition to be (current size - nixos_bytes).
+# We want the new Windows partition to be (current size - shrink_bytes).
 win_size_bytes=$(lsblk -ndo SIZE -b "$WIN_PART")
-new_win_bytes=$(( win_size_bytes - nixos_bytes ))
+new_win_bytes=$(( win_size_bytes - shrink_bytes ))
 ntfsresize -s --size "$new_win_bytes" "$WIN_PART" 2>&1 | tail -5 \
   || fail "ntfsresize failed; aborting"
 
@@ -137,24 +151,78 @@ ntfsresize -s --size "$new_win_bytes" "$WIN_PART" 2>&1 | tail -5 \
 partprobe "$DISK"
 sleep 2
 
-# === Find next available partition number ===
-existing=$(lsblk -nlo NAME "$DISK" 2>/dev/null | wc -l)
-log "Existing partitions on $DISK: $existing"
+# Snapshot the partition list BEFORE we create the new ones, so we can diff
+# and identify which device nodes are new. Plain `sort | tail -1` is unsafe
+# when more than one new partition is created (NixOS root + swap).
+existing_parts=$(lsblk -nlo NAME "$DISK" 2>/dev/null | tail -n +2 | sort)
 
-# Create NixOS root partition in the freed space
-log "Creating NixOS root partition ($NIXOS_SIZE)..."
-parted -s -a opt "$DISK" mkpart primary ext4 -- -"$NIXOS_SIZE" 100% || fail "parted mkpart failed"
+# === Create NixOS root + swap in the freed space ===
+# Compute the start = end of the (now smaller) Windows partition.
+# We deliberately do NOT use `-NIXOS_SIZE 100%` because on a T490 the recovery
+# partition sits at the end of the disk and that range would overlap it.
+# We work in 1MiB units and let parted align.
+win_new_bytes=$(lsblk -ndo SIZE -b "$WIN_PART")
+win_end_mib=$(( (win_new_bytes + 1024*1024 - 1) / (1024*1024) ))
+
+# Extract the numeric prefix of NIXOS_SIZE for the parted range calculation.
+nix_num=${NIXOS_SIZE%[GgMmKk]*}; nix_unit=${NIXOS_SIZE##*[0-9]}
+case "$nix_unit" in
+  G|g) nix_size_mib=$(( nix_num * 1024 )) ;;
+  M|m) nix_size_mib=$nix_num ;;
+  *)   fail "NIXOS_SIZE must be suffixed with M or G (got '$NIXOS_SIZE')" ;;
+esac
+nix_start_mib=$win_end_mib
+nix_end_mib=$(( nix_start_mib + nix_size_mib ))
+log "Creating NixOS root partition (${NIXOS_SIZE}) at ${nix_start_mib}MiB..${nix_end_mib}MiB..."
+parted -s "$DISK" mkpart primary ext4 "${nix_start_mib}MiB" "${nix_end_mib}MiB" \
+  || fail "parted mkpart (nixos) failed"
 partprobe "$DISK"
-sleep 2
+sleep 1
 
-# Find the new partition
-NIXOS_PART=$(lsblk -nlo NAME "$DISK" 2>/dev/null | sed "s|^|/dev/|" | sort | tail -1)
-log "New partition: $NIXOS_PART"
+if [[ "$SWAP_SIZE" != "0" ]]; then
+  swap_num=${SWAP_SIZE%[GgMmKk]*}; swap_unit=${SWAP_SIZE##*[0-9]}
+  case "$swap_unit" in
+    G|g) swap_size_mib=$(( swap_num * 1024 )) ;;
+    M|m) swap_size_mib=$swap_num ;;
+    *)   fail "SWAP_SIZE must be suffixed with M or G (got '$SWAP_SIZE')" ;;
+  esac
+  swap_end_mib=$(( nix_end_mib + swap_size_mib ))
+  log "Creating swap partition (${SWAP_SIZE}) at ${nix_end_mib}MiB..${swap_end_mib}MiB..."
+  parted -s "$DISK" mkpart primary linux-swap "${nix_end_mib}MiB" "${swap_end_mib}MiB" \
+    || fail "parted mkpart (swap) failed"
+  partprobe "$DISK"
+  sleep 1
+fi
+
+# Identify the new partitions by diffing the partition table. New partitions
+# are the ones that didn't exist before we ran mkpart.
+new_parts=$(lsblk -nlo NAME "$DISK" 2>/dev/null | tail -n +2 | sort)
+NIXOS_PART=$(comm -13 <(echo "$existing_parts") <(echo "$new_parts") \
+  | grep -v "$(basename "$DISK")" \
+  | head -1 \
+  | sed 's|^|/dev/|')
+[[ -n "$NIXOS_PART" ]] || fail "could not identify the new NixOS partition"
+log "New NixOS partition: $NIXOS_PART"
+if [[ "$SWAP_SIZE" != "0" ]]; then
+  SWAP_PART=$(comm -13 <(echo "$existing_parts") <(echo "$new_parts") \
+    | grep -v "$NIXOS_PART" \
+    | grep -v "$(basename "$DISK")" \
+    | head -1 \
+    | sed 's|^|/dev/|')
+  [[ -n "$SWAP_PART" ]] || fail "could not identify the new swap partition"
+  log "New swap partition: $SWAP_PART"
+fi
 
 # === Format and mount ===
 log "Formatting $NIXOS_PART as ext4..."
 mkfs.ext4 -F -L nixos "$NIXOS_PART"
 
+if [[ "$SWAP_SIZE" != "0" ]]; then
+  log "Setting up swap on $SWAP_PART..."
+  mkswap -L swap "$SWAP_PART"
+  swapon "$SWAP_PART"
+fi
+
 log "Mounting..."
 mount "$NIXOS_PART" /mnt
 mkdir -p /mnt/boot