diff --git a/examples/01_simple_type_checking/01_simple_operations.py b/examples/01_simple_type_checking/01_simple_operations.py
index a3ac707..4e767f2 100644
--- a/examples/01_simple_type_checking/01_simple_operations.py
+++ b/examples/01_simple_type_checking/01_simple_operations.py
@@ -9,3 +9,5 @@ d = True
 e = d + d
 
 f: float = a
+
+f = -f
diff --git a/examples/01_simple_type_checking/02_simple_types.midas b/examples/01_simple_type_checking/02_simple_types.midas
index 6a1a6a2..ff4edb1 100644
--- a/examples/01_simple_type_checking/02_simple_types.midas
+++ b/examples/01_simple_type_checking/02_simple_types.midas
@@ -3,12 +3,12 @@ type Second = float
 type MeterPerSecond = float
 
 extend Meter {
-    op __add__(Meter) -> Meter
-    op __sub__(Meter) -> Meter
-    op __truediv__(Second) -> MeterPerSecond
+    def __add__: fn(Meter, /) -> Meter
+    def __sub__: fn(Meter, /) -> Meter
+    def __truediv__: fn(Second, /) -> MeterPerSecond
 }
 
 extend Second {
-    op __add__(Second) -> Second
-    op __sub__(Second) -> Second
+    def __add__: fn(Second, /) -> Second
+    def __sub__: fn(Second, /) -> Second
 }
diff --git a/midas/checker/operators.py b/midas/checker/operators.py
index e65ab07..58af88c 100644
--- a/midas/checker/operators.py
+++ b/midas/checker/operators.py
@@ -29,3 +29,10 @@ COMPARATOR_METHODS: dict[Type[ast.cmpop], str] = {
     # ast.In: "__in__",
     # ast.NotIn: "__notin__",
 }
+
+UNARY_METHODS: dict[Type[ast.unaryop], str] = {
+    ast.Invert: "__invert__",
+    # ast.Not: "",
+    ast.UAdd: "__pos__",
+    ast.USub: "__neg__",
+}
diff --git a/midas/checker/python.py b/midas/checker/python.py
index 5149bb7..9c788c8 100644
--- a/midas/checker/python.py
+++ b/midas/checker/python.py
@@ -6,7 +6,7 @@ from typing import Optional
 import midas.ast.python as p
 from midas.ast.location import Location
 from midas.checker.environment import Environment
-from midas.checker.operators import COMPARATOR_METHODS, OPERATOR_METHODS
+from midas.checker.operators import COMPARATOR_METHODS, OPERATOR_METHODS, UNARY_METHODS
 from midas.checker.registry import TypesRegistry
 from midas.checker.reporter import FileReporter, Reporter
 from midas.checker.resolver import Resolver
@@ -376,8 +376,37 @@ class PythonTyper(
                 return UnknownType()
 
     def visit_unary_expr(self, expr: p.UnaryExpr) -> Type:
-        self.reporter.warning(expr.location, "UnaryExpr not yet supported")
-        return UnknownType()
+        method: Optional[str] = UNARY_METHODS.get(expr.operator.__class__)
+        if method is None:
+            self.logger.warning(f"Unsupported operator {expr.operator}")
+            self.reporter.warning(
+                expr.location, f"Unsupported operator {expr.operator}"
+            )
+            return UnknownType()
+
+        operand: Type = self.type_of(expr.right)
+        operation: Optional[Type] = self.types.lookup_member(operand, method)
+        if operation is None:
+            self.reporter.error(
+                expr.location,
+                f"Undefined operation {method} for {operand}",
+            )
+            return UnknownType()
+
+        match operation:
+            case Function() as function:
+                if not self._is_unary_function(function):
+                    self.reporter.error(
+                        expr.location,
+                        f"Wrong definition of unary operation. Expected function with 0 parameters, got {function}",
+                    )
+                    return UnknownType()
+                return function.returns
+            case _:
+                self.reporter.warning(
+                    expr.location, f"Unsupported operation {operation}"
+                )
+                return UnknownType()
 
     def visit_call_expr(self, expr: p.CallExpr) -> Type:
         callee: Type = self.type_of(expr.callee)
@@ -633,3 +662,12 @@ class PythonTyper(
         if len(function.kw_args) != 0:
             return False
         return True
+
+    def _is_unary_function(self, function: Function) -> bool:
+        if len(function.pos_args) != 0:
+            return False
+        if len(function.args) != 0:
+            return False
+        if len(function.kw_args) != 0:
+            return False
+        return True