diff --git a/cast.sh b/cast.sh
index 17bf79e..c9e5eeb 100644
--- a/cast.sh
+++ b/cast.sh
@@ -145,9 +145,27 @@ install_plugins() {
 
 # 🐚 Ask to set Fish as default shell (only if not already)
 set_fish_default() {
-    local fish_path current_shell
+    local fish_path current_shell confirm
+
     fish_path="$(command -v fish)"
-    current_shell="$(getent passwd "$USER" | cut -d: -f7)"
+
+    if [[ -z "$fish_path" ]]; then
+        echo "✗ Fish is not installed or not in PATH"
+        return 1
+    fi
+
+    # Detect the user's configured login shell in a cross-platform way
+    if command -v getent >/dev/null 2>&1; then
+        # Linux / glibc systems
+        current_shell="$(getent passwd "$USER" | cut -d: -f7)"
+    elif command -v dscl >/dev/null 2>&1; then
+        # macOS
+        current_shell="$(dscl . -read "/Users/$USER" UserShell 2>/dev/null | awk '{print $2}')"
+    else
+        # Fallback: try /etc/passwd, then SHELL env var
+        current_shell="$(awk -F: -v user="$USER" '$1 == user {print $7}' /etc/passwd 2>/dev/null)"
+        [[ -z "$current_shell" ]] && current_shell="$SHELL"
+    fi
 
     if [[ "$current_shell" == "$fish_path" ]]; then
         echo "✓ Fish is already your default shell"
@@ -156,11 +174,19 @@ set_fish_default() {
 
     read -rp "Set Fish as your default shell? (y/N): " confirm
     if [[ "$confirm" =~ ^[Yy]$ ]]; then
-        if ! grep -q "^$fish_path$" /etc/shells; then
-            echo "$fish_path" | sudo tee -a /etc/shells >/dev/null
+        # Only try to add to /etc/shells if that file exists
+        if [[ -f /etc/shells ]]; then
+            if ! grep -qx "$fish_path" /etc/shells; then
+                echo "$fish_path" | sudo tee -a /etc/shells >/dev/null
+            fi
+        fi
+
+        if chsh -s "$fish_path"; then
+            echo "✓ Fish set as default shell (applies to new sessions)"
+        else
+            echo "✗ Failed to set Fish as default shell"
+            return 1
         fi
-        chsh -s "$fish_path"
-        echo "✓ Fish set as default shell (applies to new sessions)"
     else
         echo "✓ Keeping current default shell"
     fi