diff --git a/mitmproxy/addons/errorcheck.py b/mitmproxy/addons/errorcheck.py
index 4143a172c..6669ee435 100644
--- a/mitmproxy/addons/errorcheck.py
+++ b/mitmproxy/addons/errorcheck.py
@@ -1,6 +1,5 @@
 import asyncio
 import sys
-from typing import Optional
 
 from mitmproxy import log
 
@@ -9,12 +8,12 @@ class ErrorCheck:
     """Monitor startup for error log entries, and terminate immediately if there are some."""
 
     def __init__(self, log_to_stderr: bool = False):
-        self.has_errored: Optional[str] = None
+        self.has_errored: list[str] = []
         self.log_to_stderr = log_to_stderr
 
     def add_log(self, e: log.LogEntry):
-        if not self.has_errored and e.level == "error":
-            self.has_errored = e.msg
+        if e.level == "error":
+            self.has_errored.append(e.msg)
 
     async def running(self):
         # don't run immediately, wait for all logging tasks to finish.
@@ -23,5 +22,8 @@ class ErrorCheck:
     async def _shutdown_if_errored(self):
         if self.has_errored:
             if self.log_to_stderr:
-                print(f"Error on startup: {self.has_errored}", file=sys.stderr)
+                plural = "s" if len(self.has_errored) > 1 else ""
+                msg = "\n".join(self.has_errored)
+                print(f"Error{plural} on startup: {msg}", file=sys.stderr)
+
             sys.exit(1)
diff --git a/mitmproxy/master.py b/mitmproxy/master.py
index 3925602ad..ec10032c0 100644
--- a/mitmproxy/master.py
+++ b/mitmproxy/master.py
@@ -46,9 +46,11 @@ class Master:
             # Handle scheduled tasks (configure()) first.
             await asyncio.sleep(0)
             await self.running()
-            await self.should_exit.wait()
-
-            await self.done()
+            try:
+                await self.should_exit.wait()
+            finally:
+                # .wait might be cancelled (e.g. by sys.exit)
+                await self.done()
         finally:
             self.event_loop.set_exception_handler(old_handler)