diff --git a/opshin/tests/test_keywords.py b/opshin/tests/test_keywords.py
index 91957733..271498d3 100644
--- a/opshin/tests/test_keywords.py
+++ b/opshin/tests/test_keywords.py
@@ -96,3 +96,34 @@ def validator(a: int, b: int, c: int) -> int:
 """
         ret = eval_uplc_value(source_code, x, y, z)
         self.assertEqual(ret, (x - z) * y)
+
+    @given(x=st.integers(), y=st.integers(), z=st.integers())
+    def test_default(self, x: int, y: int, z: int):
+        source_code = f"""
+def simple_example(x: int, y: int, z: int={z}) -> int:
+    return (x-z)*y
+
+def validator(a: int, b: int) -> int:
+    return simple_example(a, b)
+"""
+        ret = eval_uplc_value(source_code, x, y)
+        self.assertEqual(ret, (x - z) * y)
+
+    def test_default_wrong_type(self):
+        source_code = f"""
+def simple_example(x: int, y: int, z: int="hello") -> int:
+    return (x-z)*y
+
+def validator(a: int, b: int) -> int:
+    return simple_example(a, b)
+"""
+        with self.assertRaises(Exception):
+            ret = eval_uplc_value(source_code, 1, 2)
+
+    def test_no_allow_validator_default(self):
+        source_code = f"""
+def validator(a: int, b: int, c:int=1) -> int:
+    return a*b*c
+"""
+        with self.assertRaises(Exception):
+            ret = eval_uplc_value(source_code, 1, 2, 2)
diff --git a/opshin/type_inference.py b/opshin/type_inference.py
index 5a10d064..21de5727 100644
--- a/opshin/type_inference.py
+++ b/opshin/type_inference.py
@@ -24,6 +24,14 @@
 # from frozendict import frozendict
 
 
+def pad_left(a: list, b: list, filler=None):
+    if len(a) > len(b):
+        return a, [filler for _ in range(len(a) - len(b))] + b
+    if len(b) > len(a):
+        return [filler for _ in range(len(b) - len(a))] + a, b
+    return a, b
+
+
 INITIAL_SCOPE = {
     # class annotations
     "bytes": ByteStringType(),
@@ -244,6 +252,7 @@ class AggressiveTypeInferencer(CompilingNodeTransformer):
     def __init__(self, allow_isinstance_anything=False):
         self.allow_isinstance_anything = allow_isinstance_anything
         self.FUNCTION_ARGUMENT_REGISTRY = {}
+        self.FUNCTION_DEFAULT_REGISTRY = {}
 
         # A stack of dictionaries for storing scoped knowledge of variable types
         self.scopes = [INITIAL_SCOPE]
@@ -561,12 +570,18 @@ def visit_arg(self, node: arg) -> typedarg:
         return ta
 
     def visit_arguments(self, node: arguments) -> typedarguments:
-        if node.kw_defaults or node.kwarg or node.kwonlyargs or node.defaults:
+        if node.kw_defaults or node.kwarg or node.kwonlyargs:
             raise NotImplementedError(
                 "Keyword arguments and defaults not supported yet"
             )
         ta = copy(node)
         ta.args = [self.visit(a) for a in node.args]
+        ta.defaults = [self.visit(d) for d in node.defaults]
+        # defaults match last k arguments
+        for i, (a, d) in enumerate(zip(reversed(ta.args), reversed(ta.defaults))):
+            assert (
+                a.typ >= d.typ
+            ), f'Default value must be compatible with argument in argument "{a.orig_arg}" (position {len(ta.args)-i}). Expected {a.typ}, got {d.typ}'
         return ta
 
     def visit_FunctionDef(self, node: FunctionDef) -> TypedFunctionDef:
@@ -604,7 +619,8 @@ def visit_FunctionDef(self, node: FunctionDef) -> TypedFunctionDef:
         self.exit_scope()
         # We need the function type outside for usage
         self.set_variable_type(node.name, tfd.typ)
-        self.FUNCTION_ARGUMENT_REGISTRY[node.name] = node.args.args
+        self.FUNCTION_ARGUMENT_REGISTRY[node.name] = tfd.args.args
+        self.FUNCTION_DEFAULT_REGISTRY[node.name] = tfd.args.defaults
         return tfd
 
     def visit_Module(self, node: Module) -> TypedModule:
@@ -776,8 +792,9 @@ def visit_Call(self, node: Call) -> TypedCall:
             ), "Keyword arguments can only be used with user defined functions"
             keywords = copy(node.keywords)
             reg_args = self.FUNCTION_ARGUMENT_REGISTRY[node.func.id]
+            reg_defs = self.FUNCTION_DEFAULT_REGISTRY[node.func.id]
             args = []
-            for i, a in enumerate(reg_args):
+            for i, (a, d) in enumerate(zip(*pad_left(reg_args, reg_defs))):
                 if len(node.args) > i:
                     args.append(self.visit(node.args[i]))
                 else:
@@ -786,11 +803,19 @@ def visit_Call(self, node: Call) -> TypedCall:
                         for idx, keyword in enumerate(keywords)
                         if keyword.arg == a.orig_arg
                     ]
-                    assert (
-                        len(candidates) == 1
-                    ), f"There should be one keyword or positional argument for the arg {a.orig_arg} but found {len(candidates)}"
-                    args.append(self.visit(candidates[0][1].value))
-                    keywords.pop(candidates[0][0])
+                    if candidates:
+                        assert (
+                            len(candidates) == 1
+                        ), f'There should be one keyword or positional argument for the argument "{a.orig_arg}" (position {i+1}) but found {len(candidates)}'
+                        candidate = self.visit(candidates[0][1].value)
+                        keywords.pop(candidates[0][0])
+                    elif d is not None:
+                        candidate = copy(d)
+                    else:
+                        raise AssertionError(
+                            f'Could not find argument for argument "{a.orig_arg}" (position {i+1})'
+                        )
+                    args.append(candidate)
             assert (
                 len(keywords) == 0
             ), f"Could not match the keywords {[keyword.arg for keyword in keywords]} to any argument"