diff --git a/Lib/fontTools/otlLib/builder.py b/Lib/fontTools/otlLib/builder.py
index 7711fa4c5..5d16b83c2 100644
--- a/Lib/fontTools/otlLib/builder.py
+++ b/Lib/fontTools/otlLib/builder.py
@@ -2575,7 +2575,7 @@ class ClassDefBuilder(object):
         self.classes_.add(glyphs)
         for glyph in glyphs:
             if glyph in self.glyphs_:
-                raise TypeError(f"Glyph {glyph} already present in class.")
+                raise ValueError(f"Glyph {glyph} is already present in class.")
             self.glyphs_[glyph] = glyphs
 
     def classes(self):
diff --git a/Tests/otlLib/builder_test.py b/Tests/otlLib/builder_test.py
index a2c51331d..6bd05615b 100644
--- a/Tests/otlLib/builder_test.py
+++ b/Tests/otlLib/builder_test.py
@@ -1103,15 +1103,9 @@ class ClassDefBuilderTest(object):
 
     def test_add_exception(self):
         b = builder.ClassDefBuilder(useClass0=True)
-        b.add({"a", "b", "c", "d"})
-        with pytest.raises(TypeError):
-            b.add({"a"})
-        with pytest.raises(TypeError):
-            b.add({"b"})
-        with pytest.raises(TypeError):
-            b.add({"c"})
-        with pytest.raises(TypeError):
-            b.add({"d"})
+        b.add({"a", "b", "c"})
+        with pytest.raises(ValueError):
+            b.add({"a", "d"})
 
 
 buildStatTable_test_data = [