diff --git a/giambio/_core.py b/giambio/_core.py
index 0992325..48871ff 100644
--- a/giambio/_core.py
+++ b/giambio/_core.py
@@ -107,8 +107,10 @@ class AsyncScheduler:
                         ):  # Schedules tasks that are waiting on events
                             self.check_events()
                 except CancelledError as cancelled:
-                    if cancelled.args[0] in self.tasks:
-                        self.tasks.remove(cancelled.args[0])  # Remove the dead task
+                    task = cancelled.args[0]
+                    task.cancelled = True
+                    if task in self.tasks:
+                        self.tasks.remove(task)  # Remove the dead task
                     self.tasks.append(self.current_task)
                 except StopIteration as e:  # Coroutine ends
                     self.current_task.result = e.args[0] if e.args else None
@@ -238,7 +240,9 @@ class AsyncScheduler:
     def sleep(self, seconds: int or float):
         """Puts the caller to sleep for a given amount of seconds"""
 
-        if seconds:
+        if seconds < 0:
+            raise ValueError("the delay can't be negative")
+        elif seconds:
             self.current_task.status = "sleep"
             self.paused.put(self.current_task, seconds)
         else:
@@ -276,8 +280,12 @@ class AsyncScheduler:
             "sleep",
             "I/O",
         ):  # It is safe to cancel a task while blocking
-            task.cancelled = True
-            task.throw(CancelledError(task))
+            try:
+                task.throw(CancelledError(task))
+            except Exception as error:
+                task.cancelled = True  # The task died
+                self.tasks.append(self.current_task)
+                task.exc = error
         else:
             task.status = "cancel"  # Cancellation is deferred
 
diff --git a/giambio/_managers.py b/giambio/_managers.py
index 27008ec..d6e42fe 100644
--- a/giambio/_managers.py
+++ b/giambio/_managers.py
@@ -1,5 +1,5 @@
 from ._core import AsyncScheduler
-from .exceptions import ErrorStack
+from .exceptions import ErrorStack, CancelledError
 import itertools
 
 
@@ -20,18 +20,22 @@ class TaskManager(object):
     async def _cancel_and_raise(self, err):
         """Cancels all tasks and raises an exception"""
 
-        exc = ErrorStack()
+        errors = []
         for task in itertools.chain(
             self.scheduler.tasks.copy(),
             self.scheduler.paused.items(),
-            *self.scheduler.event_waiting.values()
+            self.scheduler.event_waiting.values(),
         ):
+            await task.cancel()
             try:
-                await task.cancel()
-            except Exception as err:
-                exc.errors.append(err)
-        if exc.errors:
-            exc.errors.insert(err, 0)
+                await task.join()
+            except Exception as fault:
+                fault.__cause__ = None  # We clear this to avoid unrelated tracebacks
+                errors.append(fault)
+        if errors:
+            exc = ErrorStack()
+            errors.insert(0, err)
+            exc.errors = errors
             raise exc
         raise err
 
diff --git a/tests/raise.py b/tests/raise.py
index e60b0d6..a24e218 100644
--- a/tests/raise.py
+++ b/tests/raise.py
@@ -24,14 +24,25 @@ async def countup(stop: int, step: int = 1):
         raise ValueError("Ciao")
 
 
+async def countdown2(n: int):
+    while n > 0:
+        print(f"Down {n}")
+        n -= 1
+        await giambio.sleep(1)
+        raise Exception("bruh")
+    print("Countdown over")
+    return 0
+
+
 async def main():
     try:
         async with giambio.TaskManager(scheduler) as manager:
-            cdown = manager.create_task(countdown(10))
             cup = manager.create_task(countup(5, 2))
+            cdown = manager.create_task(countdown(10))
+#            cdown2 = manager.create_task(countdown2(5))
             print("Counters started, awaiting completion")
-    except Exception:
-        print("Exceptions propagate!")
+    except Exception as err:
+        print(f"An error occurred!\n{type(err).__name__}: {err}")
     print("Task execution complete")