diff --git a/lldb/test/Shell/Driver/TestPositionalArgs.test b/lldb/test/Shell/Driver/TestPositionalArgs.test
--- a/lldb/test/Shell/Driver/TestPositionalArgs.test
+++ b/lldb/test/Shell/Driver/TestPositionalArgs.test
@@ -23,10 +23,8 @@
 DASH: Current executable set to {{.*}}foo
 DASH: target.run-args "bar" "-baz" "--quux"
 
-RUN: %lldb -x -b %t.foo bar -baz --quux 2>&1 | FileCheck %s --check-prefix UNKNOWN
-RUN: %lldb -x -b -f %t.foo bar -baz --quux 2>&1 | FileCheck %s --check-prefix UNKNOWN
+RUN: not %lldb -x -b %t.foo bar -baz --quux 2>&1 | FileCheck %s --check-prefix UNKNOWN
+RUN: not %lldb -x -b -f %t.foo bar -baz --quux 2>&1 | FileCheck %s --check-prefix UNKNOWN
 
-UNKNOWN: warning: ignoring unknown option: -baz
-UNKNOWN: warning: ignoring unknown option: --quux
-UNKNOWN: Current executable set to {{.*}}foo
-UNKNOWN: target.run-args "bar"
+UNKNOWN: error: unknown option: -baz
+UNKNOWN: error: unknown option: --quux
diff --git a/lldb/tools/driver/Driver.cpp b/lldb/tools/driver/Driver.cpp
--- a/lldb/tools/driver/Driver.cpp
+++ b/lldb/tools/driver/Driver.cpp
@@ -856,9 +856,12 @@
     return 0;
   }
 
-  for (auto *arg : input_args.filtered(OPT_UNKNOWN)) {
-    WithColor::warning() << "ignoring unknown option: " << arg->getSpelling()
-                         << '\n';
+  // Error out on unknown options.
+  if (input_args.hasArg(OPT_UNKNOWN)) {
+    for (auto *arg : input_args.filtered(OPT_UNKNOWN)) {
+      WithColor::error() << "unknown option: " << arg->getSpelling() << '\n';
+    }
+    return 1;
   }
 
   if (auto exit_code = InitializeReproducer(input_args)) {