diff --git a/un.cpp b/un.cpp
index 0b8a5cf..04dae73 100644
--- a/un.cpp
+++ b/un.cpp
@@ -689,7 +689,11 @@ int main(int argc, char* argv[]) {
         else if (arg == "-n" && i+1 < argc) network = argv[++i];
         else if (arg == "-v" && i+1 < argc) vcpu = stoi(argv[++i]);
         else if (arg == "-k" && i+1 < argc) public_key = argv[++i];
-        else if (arg[0] != '-') source_file = arg;
+        else if (arg[0] == '-') {
+            cerr << RED << "Unknown option: " << arg << RESET << endl;
+            return 1;
+        }
+        else source_file = arg;
     }
 
     if (source_file.empty()) {
diff --git a/un.cr b/un.cr
index a49a75b..885c08e 100644
--- a/un.cr
+++ b/un.cr
@@ -615,7 +615,12 @@ def main
         when "key"
           args[:command] = "key"
         else
-          args[:source_file] = before[0]
+          if before[0].starts_with?("-")
+            STDERR.puts "#{RED}Unknown option: #{before[0]}#{RESET}"
+            exit 1
+          else
+            args[:source_file] = before[0]
+          end
         end
       end
     end
diff --git a/un.d b/un.d
index da20c99..7031f42 100644
--- a/un.d
+++ b/un.d
@@ -617,7 +617,11 @@ int main(string[] args) {
         else if (args[i] == "-n" && i+1 < args.length) network = args[++i];
         else if (args[i] == "-v" && i+1 < args.length) vcpu = to!int(args[++i]);
         else if (args[i] == "-k" && i+1 < args.length) publicKey = args[++i];
-        else if (!args[i].startsWith("-")) sourceFile = args[i];
+        else if (args[i].startsWith("-")) {
+            stderr.writefln("%sUnknown option: %s%s", RED, args[i], RESET);
+            return 1;
+        }
+        else sourceFile = args[i];
     }
 
     if (sourceFile.empty) {
diff --git a/un.dart b/un.dart
index e619cce..ddb8739 100644
--- a/un.dart
+++ b/un.dart
@@ -656,7 +656,10 @@ Args parseArgs(List<String> argv) {
         args.keyExtend = true;
         break;
       default:
-        if (!argv[i].startsWith('-')) {
+        if (argv[i].startsWith('-')) {
+          stderr.writeln('${RED}Unknown option: ${argv[i]}${RESET}');
+          exit(1);
+        } else {
           args.sourceFile = argv[i];
         }
     }
diff --git a/un.groovy b/un.groovy
index 1487c47..cfc4c99 100644
--- a/un.groovy
+++ b/un.groovy
@@ -711,7 +711,10 @@ def parseArgs(argv) {
                 args.keyExtend = true
                 break
             default:
-                if (!argv[i].startsWith('-')) {
+                if (argv[i].startsWith('-')) {
+                    System.err.println("${RED}Unknown option: ${argv[i]}${RESET}")
+                    System.exit(1)
+                } else {
                     args.sourceFile = argv[i]
                 }
         }
diff --git a/un.hs b/un.hs
index c97a45f..b689e29 100644
--- a/un.hs
+++ b/un.hs
@@ -227,7 +227,10 @@ parseExecute args =
       | "-o" `isPrefixOf` arg = parseExecArgs rest opts { exOutDir = Just (head rest) }
       | "-n" `isPrefixOf` arg = parseExecArgs rest opts { exNetwork = Just (head rest) }
       | "-v" `isPrefixOf` arg = parseExecArgs rest opts { exVcpu = Just (read (head rest)) }
-      | not ("-" `isPrefixOf` arg) && null (exFile opts) = parseExecArgs rest opts { exFile = arg }
+      | "-" `isPrefixOf` arg = do
+        hPutStrLn stderr $ red ++ "Unknown option: " ++ arg ++ reset
+        exitFailure
+      | null (exFile opts) = parseExecArgs rest opts { exFile = arg }
       | otherwise = parseExecArgs rest opts
     parseEnv (kv:rest) =
       let (k, v) = span (/= '=') kv
diff --git a/un.kt b/un.kt
index b022a13..607af87 100644
--- a/un.kt
+++ b/un.kt
@@ -748,7 +748,14 @@ fun parseArgs(args: Array<String>): Args {
             "--dump-bootstrap" -> result.serviceDumpBootstrap = args[++i]
             "--dump-file" -> result.serviceDumpFile = args[++i]
             "--extend" -> result.keyExtend = true
-            else -> if (!args[i].startsWith("-")) result.sourceFile = args[i]
+            else -> {
+                if (args[i].startsWith("-")) {
+                    System.err.println("${RED}Unknown option: ${args[i]}${RESET}")
+                    kotlin.system.exitProcess(1)
+                } else {
+                    result.sourceFile = args[i]
+                }
+            }
         }
         i++
     }
diff --git a/un.lua b/un.lua
index 3acd1c4..3cb4c0e 100644
--- a/un.lua
+++ b/un.lua
@@ -764,7 +764,10 @@ local function main()
             options.dump_file = arg[i]
         elseif a == "--extend" then
             options.extend = true
-        elseif not a:match("^%-") then
+        elseif a:match("^%-") then
+            io.stderr:write(RED .. "Unknown option: " .. a .. RESET .. "\n")
+            os.exit(1)
+        else
             options.source_file = a
         end
 
diff --git a/un.m b/un.m
index 659518e..83dce34 100644
--- a/un.m
+++ b/un.m
@@ -232,6 +232,9 @@ void cmdExecute(NSArray* args) {
             network = args[++i];
         } else if ([arg isEqualToString:@"-v"] && i + 1 < [args count]) {
             vcpu = [args[++i] intValue];
+        } else if ([arg hasPrefix:@"-"]) {
+            fprintf(stderr, "%sUnknown option: %s%s\n", RED, [arg UTF8String], RESET);
+            exit(1);
         } else {
             sourceFile = arg;
         }
diff --git a/un.nim b/un.nim
index dafe71a..f92a325 100644
--- a/un.nim
+++ b/un.nim
@@ -521,7 +521,10 @@ proc main() =
     of "-v": vcpu = parseInt(args[i+1]); inc i
     of "-k": publicKey = args[i+1]; inc i
     else:
-      if not args[i].startsWith("-"):
+      if args[i].startsWith("-"):
+        stderr.writeLine(RED & "Unknown option: " & args[i] & RESET)
+        quit(1)
+      else:
         sourceFile = args[i]
     inc i
 
diff --git a/un.php b/un.php
index 840c8e9..2626c3a 100755
--- a/un.php
+++ b/un.php
@@ -722,7 +722,10 @@ function main() {
                 $options['extend'] = true;
                 break;
             default:
-                if (!str_starts_with($arg, '-')) {
+                if (str_starts_with($arg, '-')) {
+                    fwrite(STDERR, RED . "Unknown option: $arg" . RESET . "\n");
+                    exit(1);
+                } else {
                     $options['source_file'] = $arg;
                 }
                 break;
diff --git a/un.pl b/un.pl
index e8d77ef..7b7e13b 100644
--- a/un.pl
+++ b/un.pl
@@ -643,7 +643,10 @@ sub main {
             $options{dump_file} = $ARGV[++$i];
         } elsif ($arg eq '--extend') {
             $options{extend} = 1;
-        } elsif ($arg !~ /^-/) {
+        } elsif ($arg =~ /^-/) {
+            print STDERR "${RED}Unknown option: $arg${RESET}\n";
+            exit 1;
+        } else {
             $options{source_file} = $arg;
         }
     }
diff --git a/un.ps1 b/un.ps1
index 3538602..53050cc 100644
--- a/un.ps1
+++ b/un.ps1
@@ -486,7 +486,10 @@ if ($args[0] -eq "session") {
             }
             "-n" { $network = $args[$i+1]; $i++ }
             default {
-                if (-not $args[$i].StartsWith("-")) {
+                if ($args[$i].StartsWith("-")) {
+                    Write-Error "${RED}Unknown option: $($args[$i])${RESET}"
+                    exit 1
+                } else {
                     $sourceFile = $args[$i]
                 }
             }
diff --git a/un.raku b/un.raku
index cd2082c..d4f41e6 100644
--- a/un.raku
+++ b/un.raku
@@ -201,7 +201,12 @@ sub cmd-execute(@args) {
                 $vcpu = @args[$i].Int;
             }
             default {
-                $source-file = @args[$i];
+                if @args[$i].starts-with('-') {
+                    note "$RED\Unknown option: {@args[$i]}$RESET";
+                    exit 1;
+                } else {
+                    $source-file = @args[$i];
+                }
             }
         }
         $i++;
diff --git a/un.rb b/un.rb
index 048656c..461490b 100644
--- a/un.rb
+++ b/un.rb
@@ -643,7 +643,12 @@ def main
     when '--extend'
       options[:extend] = true
     else
-      options[:source_file] = arg unless arg.start_with?('-')
+      if arg.start_with?('-')
+        warn "#{RED}Unknown option: #{arg}#{RESET}"
+        exit 1
+      else
+        options[:source_file] = arg
+      end
     end
 
     i += 1
diff --git a/un.rs b/un.rs
index f7830ba..57031a7 100644
--- a/un.rs
+++ b/un.rs
@@ -825,7 +825,10 @@ fn main() {
                 return;
             }
             _ => {
-                if !args[i].starts_with('-') {
+                if args[i].starts_with('-') {
+                    eprintln!("{}Unknown option: {}{}", RED, args[i], RESET);
+                    std::process::exit(1);
+                } else {
                     source_file = Some(args[i].clone());
                 }
             }
diff --git a/un.sh b/un.sh
index 8d20caa..169bd6d 100755
--- a/un.sh
+++ b/un.sh
@@ -247,6 +247,10 @@ cmd_execute() {
                 api_key="$2"
                 shift 2
                 ;;
+            -*)
+                echo -e "${RED}Unknown option: $1${RESET}" >&2
+                exit 1
+                ;;
             *)
                 source_file="$1"
                 shift
@@ -391,6 +395,10 @@ cmd_session() {
                 api_key="$2"
                 shift 2
                 ;;
+            -*)
+                echo -e "${RED}Unknown option: $1${RESET}" >&2
+                exit 1
+                ;;
             *)
                 shift
                 ;;
@@ -562,6 +570,10 @@ cmd_service() {
                 api_key="$2"
                 shift 2
                 ;;
+            -*)
+                echo -e "${RED}Unknown option: $1${RESET}" >&2
+                exit 1
+                ;;
             *)
                 shift
                 ;;
@@ -850,6 +862,10 @@ cmd_key() {
                 extend=true
                 shift
                 ;;
+            -*)
+                echo -e "${RED}Unknown option: $1${RESET}" >&2
+                exit 1
+                ;;
             *)
                 shift
                 ;;
diff --git a/un.v b/un.v
index 08bfe91..23e7bff 100644
--- a/un.v
+++ b/un.v
@@ -698,7 +698,10 @@ fn main() {
 				api_key = os.args[i]
 			}
 			else {
-				if !os.args[i].starts_with('-') {
+				if os.args[i].starts_with('-') {
+					eprintln('${red}Unknown option: ${os.args[i]}${reset}')
+					exit(1)
+				} else {
 					source_file = os.args[i]
 				}
 			}
diff --git a/un.zig b/un.zig
index ed9e93c..b67e73f 100644
--- a/un.zig
+++ b/un.zig
@@ -621,7 +621,11 @@ pub fn main() !u8 {
     // Execute mode - find source file
     var source_file: ?[]const u8 = null;
     for (args[1..]) |arg| {
-        if (!mem.startsWith(u8, arg, "-")) {
+        if (mem.startsWith(u8, arg, "-")) {
+            const stderr = std.io.getStdErr().writer();
+            stderr.print("{s}Unknown option: {s}{s}\n", .{ RED, arg, RESET }) catch {};
+            std.os.exit(1);
+        } else {
             source_file = arg;
             break;
         }