diff --git a/spec/propane_spec.rb b/spec/propane_spec.rb
index d83f1c1..f31bc14 100644
--- a/spec/propane_spec.rb
+++ b/spec/propane_spec.rb
@@ -81,6 +81,29 @@ EOF
     expect(results.status).to eq 0
   end
 
+  it "detects a lexer error when an unknown character is seen" do
+    write_grammar <<EOF
+ptype int;
+token int /\\d+/ <<
+  int v;
+  foreach (c; match)
+  {
+    v *= 10;
+    v += (c - '0');
+  }
+  $$ = v;
+>>
+Start -> int <<
+  $$ = $1;
+>>
+EOF
+    build_parser
+    compile("spec/test_lexer_unknown_character.d")
+    results = run
+    expect(results.stderr).to eq ""
+    expect(results.status).to eq 0
+  end
+
   it "generates a parser" do
     write_grammar <<EOF
 token plus /\\+/;
diff --git a/spec/test_lexer_unknown_character.d b/spec/test_lexer_unknown_character.d
new file mode 100644
index 0000000..d31cb05
--- /dev/null
+++ b/spec/test_lexer_unknown_character.d
@@ -0,0 +1,19 @@
+import testparser;
+import std.stdio;
+
+int main()
+{
+    return 0;
+}
+
+unittest
+{
+    string input = `x`;
+    auto parser = new Testparser.Parser(input);
+    assert(parser.parse() == Testparser.P_UNEXPECTED_INPUT);
+
+    input = `123`;
+    parser = new Testparser.Parser(input);
+    assert(parser.parse() == Testparser.P_SUCCESS);
+    assert(parser.result == 123u);
+}