diff --git a/artiq/language/environment.py b/artiq/language/environment.py
index 766779177..eff9fc3f1 100644
--- a/artiq/language/environment.py
+++ b/artiq/language/environment.py
@@ -32,7 +32,7 @@ class _SimpleArgProcessor:
         if isinstance(default, list):
             raise NotImplementedError
         if default is not NoDefault:
-            self.default_value = default
+            self.default_value = self.process(default)
 
     def default(self):
         if not hasattr(self, "default_value"):
@@ -54,6 +54,7 @@ class PYONValue(_SimpleArgProcessor):
     def __init__(self, default=NoDefault):
         # Override the _SimpleArgProcessor init, as list defaults are valid
         # PYON values
+        # default stays decoded
         if default is not NoDefault:
             self.default_value = default
 
@@ -69,7 +70,13 @@ class PYONValue(_SimpleArgProcessor):
 
 class BooleanValue(_SimpleArgProcessor):
     """A boolean argument."""
-    pass
+    def process(self, x):
+        if x is True:
+            return True
+        elif x is False:
+            return False
+        else:
+            raise ValueError("Invalid BooleanValue value")
 
 
 class EnumerationValue(_SimpleArgProcessor):
@@ -80,15 +87,20 @@ class EnumerationValue(_SimpleArgProcessor):
         argument.
     """
     def __init__(self, choices, default=NoDefault):
-        _SimpleArgProcessor.__init__(self, default)
-        assert default is NoDefault or default in choices
         self.choices = choices
+        super().__init__(default)
+
+    def process(self, x):
+        if x not in self.choices:
+            raise ValueError("Invalid EnumerationValue value")
+        return x
 
     def describe(self):
         d = _SimpleArgProcessor.describe(self)
         d["choices"] = self.choices
         return d
 
+
 class NumberValue(_SimpleArgProcessor):
     """An argument that can take a numerical value.
 
@@ -132,8 +144,6 @@ class NumberValue(_SimpleArgProcessor):
                                    "the scale manually".format(unit))
         if step is None:
             step = scale/10.0
-        if default is not NoDefault:
-            self.default_value = default
         self.unit = unit
         self.scale = scale
         self.step = step
@@ -141,19 +151,13 @@ class NumberValue(_SimpleArgProcessor):
         self.max = max
         self.ndecimals = ndecimals
 
+        super().__init__(default)
+
     def _is_int(self):
         return (self.ndecimals == 0
                 and int(self.step) == self.step
                 and self.scale == 1)
 
-    def default(self):
-        if not hasattr(self, "default_value"):
-            raise DefaultMissing
-        if self._is_int():
-            return int(self.default_value)
-        else:
-            return float(self.default_value)
-
     def process(self, x):
         if self._is_int():
             return int(x)
diff --git a/artiq/test/test_arguments.py b/artiq/test/test_arguments.py
new file mode 100644
index 000000000..884c8982f
--- /dev/null
+++ b/artiq/test/test_arguments.py
@@ -0,0 +1,79 @@
+import unittest
+import numbers
+
+
+from artiq.language.environment import BooleanValue, EnumerationValue, \
+     NumberValue, DefaultMissing
+
+
+class NumberValueCase(unittest.TestCase):
+    def setUp(self):
+        self.default_value = NumberValue()
+        self.int_value = NumberValue(42, step=1, ndecimals=0)
+        self.float_value = NumberValue(42)
+
+    def test_invalid_default(self):
+        with self.assertRaises(ValueError):
+            _ = NumberValue("invalid")
+
+        with self.assertRaises(TypeError):
+            _ = NumberValue(1.+1j)
+
+    def test_no_default(self):
+        with self.assertRaises(DefaultMissing):
+            self.default_value.default()
+
+    def test_integer_default(self):
+        self.assertIsInstance(self.int_value.default(), numbers.Integral)
+
+    def test_default_to_float(self):
+        self.assertIsInstance(self.float_value.default(), numbers.Real)
+        self.assertNotIsInstance(self.float_value.default(), numbers.Integral)
+
+    def test_invalid_unit(self):
+        with self.assertRaises(KeyError):
+            _ = NumberValue(unit="invalid")
+
+    def test_default_scale(self):
+        self.assertEqual(self.default_value.scale, 1.)
+
+
+class BooleanValueCase(unittest.TestCase):
+    def setUp(self):
+        self.default_value = BooleanValue()
+        self.true_value = BooleanValue(True)
+        self.false_value = BooleanValue(False)
+
+    def test_default(self):
+        self.assertIs(self.true_value.default(), True)
+        self.assertIs(self.false_value.default(), False)
+
+    def test_no_default(self):
+        with self.assertRaises(DefaultMissing):
+            self.default_value.default()
+
+    def test_invalid_default(self):
+        with self.assertRaises(ValueError):
+            _ = BooleanValue(1)
+
+        with self.assertRaises(ValueError):
+            _ = BooleanValue("abc")
+
+
+class EnumerationValueCase(unittest.TestCase):
+    def setUp(self):
+        self.default_value = EnumerationValue(["abc"])
+
+    def test_no_default(self):
+        with self.assertRaises(DefaultMissing):
+            self.default_value.default()
+
+    def test_invalid_default(self):
+        with self.assertRaises(ValueError):
+            _ = EnumerationValue("abc", "d")
+
+    def test_valid_default(self):
+        try:
+            _ = EnumerationValue("abc", "a")
+        except ValueError:
+            self.fail("Unexpected ValueError")