diff --git a/changelog.d/15599.bugfix b/changelog.d/15599.bugfix
new file mode 100644
index 0000000000..b58af8ad55
--- /dev/null
+++ b/changelog.d/15599.bugfix
@@ -0,0 +1 @@
+Print full error and stack-trace of any exception that occurs during startup/initialization.
diff --git a/synapse/app/_base.py b/synapse/app/_base.py
index 4dfcf484fa..936b1b0430 100644
--- a/synapse/app/_base.py
+++ b/synapse/app/_base.py
@@ -214,7 +214,7 @@ def handle_startup_exception(e: Exception) -> NoReturn:
     # the reactor are written to the logs, followed by a summary to stderr.
     logger.exception("Exception during startup")
 
-    error_string = "".join(traceback.format_exception(e))
+    error_string = "".join(traceback.format_exception(type(e), e, e.__traceback__))
     indented_error_string = indent(error_string, "    ")
 
     quit_with_error(