diff --git a/Lib/fontTools/otlLib/optimize/__init__.py b/Lib/fontTools/otlLib/optimize/__init__.py
index d39bb28d1..5c007e891 100644
--- a/Lib/fontTools/otlLib/optimize/__init__.py
+++ b/Lib/fontTools/otlLib/optimize/__init__.py
@@ -51,7 +51,8 @@ def main(args=None):
     )
 
     font = TTFont(options.font)
-    compact(font, options.gpos_compact_mode)
+    # TODO: switch everything to have type(mode) = int when using the Config class
+    compact(font, str(options.gpos_compact_mode))
     font.save(options.outfile or options.font)
 
 
diff --git a/Tests/otlLib/optimize_test.py b/Tests/otlLib/optimize_test.py
index c2f2468eb..4201aed09 100644
--- a/Tests/otlLib/optimize_test.py
+++ b/Tests/otlLib/optimize_test.py
@@ -7,10 +7,12 @@ from fontTools.fontBuilder import FontBuilder
 
 def test_main(tmpdir: Path):
     """Check that calling the main function on an input TTF works."""
-    glyphs = ".notdef space A B".split()
+    glyphs = ".notdef space A Aacute B D".split()
     features = """
+    @A = [A Aacute];
+    @B = [B D];
     feature kern {
-        pos A B -50;
+        pos @A @B -50;
     } kern;
     """
     fb = FontBuilder(1000)
@@ -32,3 +34,21 @@ def test_main(tmpdir: Path):
         check=True,
     )
     assert output.exists()
+
+
+def test_off_by_default(tmpdir: Path):
+    """Check that calling the main function on an input TTF works."""
+    glyphs = ".notdef space A B".split()
+    features = """
+    feature kern {
+        pos A B -50;
+    } kern;
+    """
+    fb = FontBuilder(1000)
+    fb.setupGlyphOrder(glyphs)
+    addOpenTypeFeaturesFromString(fb.font, features)
+    input = tmpdir / "in.ttf"
+    fb.save(str(input))
+    output = tmpdir / "out.ttf"
+    run(["fonttools", "otlLib.optimize", str(input), "-o", str(output)], check=True)
+    assert output.exists()