diff --git a/docs/news.rst b/docs/news.rst
index 8c94659b..5b1f6678 100644
--- a/docs/news.rst
+++ b/docs/news.rst
@@ -26,7 +26,11 @@ API
 ^^^
 
 - If the ``egg`` parameter to the :ref:`addversion.json`` webservice is not a ZIP file, use the error message, "egg is not a ZIP file (if using curl, use egg=@path not egg=path)".
-- Clarify some error messages: for example, ``'project' parameter is required`` instead of ``'project'``, and ``exception class: message`` instead of ``message``.
+- Clarify some error messages, for example:
+
+  - ``'project' parameter is required`` instead of ``'project'``
+  - ``exception class: message`` instead of ``message``
+  - ``ValueError: Unknown or corrupt egg`` instead of ``TypeError: 'tuple' object is not an iterator``
 
 CLI
 ^^^
diff --git a/scrapyd/eggutils.py b/scrapyd/eggutils.py
index 92f99182..87ef6bc2 100644
--- a/scrapyd/eggutils.py
+++ b/scrapyd/eggutils.py
@@ -8,8 +8,11 @@ def activate_egg(eggpath):
     to activate a Scrapy egg file. Don't use it from other code as it may
     leave unwanted side effects.
     """
+    distributions = pkg_resources.find_distributions(eggpath)
+    if isinstance(distributions, tuple):
+        raise ValueError("Unknown or corrupt egg")
     try:
-        d = next(pkg_resources.find_distributions(eggpath))
+        d = next(distributions)
     except StopIteration:
         raise ValueError("Unknown or corrupt egg")
     d.activate()
diff --git a/scrapyd/exceptions.py b/scrapyd/exceptions.py
index f75b5045..5db6ab49 100644
--- a/scrapyd/exceptions.py
+++ b/scrapyd/exceptions.py
@@ -4,3 +4,7 @@ class ScrapydError(Exception):
 
 class MissingRequiredArgument(ScrapydError):
     """Raised if a required argument is missing"""
+
+
+class RunnerError(ScrapydError):
+    """Raised if the runner returns an error code"""
diff --git a/scrapyd/tests/test_utils.py b/scrapyd/tests/test_utils.py
index aa8b5d46..41a80267 100644
--- a/scrapyd/tests/test_utils.py
+++ b/scrapyd/tests/test_utils.py
@@ -10,6 +10,7 @@
 from twisted.trial import unittest
 
 from scrapyd import get_application
+from scrapyd.exceptions import RunnerError
 from scrapyd.interfaces import IEggStorage
 from scrapyd.utils import UtilsCache, get_crawl_args, get_spider_list, sorted_versions
 
@@ -123,7 +124,7 @@ def popen_wrapper(*args, **kwargs):
             return Popen(cmd, *args, **kwargs)
 
         with mock.patch('scrapyd.utils.Popen', wraps=popen_wrapper):
-            exc = self.assertRaises(RuntimeError, get_spider_list, 'mybot3', pythonpath=pypath)
+            exc = self.assertRaises(RunnerError, get_spider_list, 'mybot3', pythonpath=pypath)
         self.assertRegex(str(exc).rstrip(), r'Exception: This should break the `scrapy list` command$')
 
 
diff --git a/scrapyd/utils.py b/scrapyd/utils.py
index baf26fc5..2002a7bf 100644
--- a/scrapyd/utils.py
+++ b/scrapyd/utils.py
@@ -9,6 +9,7 @@
 from twisted.web import resource
 
 from scrapyd.config import Config
+from scrapyd.exceptions import RunnerError
 from scrapyd.sqlite import JsonSqliteDict
 
 
@@ -139,7 +140,7 @@ def get_spider_list(project, runner=None, pythonpath=None, version=''):
     if proc.returncode:
         msg = err or out or ''
         msg = msg.decode('utf8')
-        raise RuntimeError(msg)
+        raise RunnerError(msg)
     # FIXME: can we reliably decode as UTF-8?
     # scrapy list does `print(list)`
     tmp = out.decode('utf-8').splitlines()
diff --git a/scrapyd/webservice.py b/scrapyd/webservice.py
index 09da9918..5f059da7 100644
--- a/scrapyd/webservice.py
+++ b/scrapyd/webservice.py
@@ -118,9 +118,10 @@ def render_POST(self, txrequest):
 class AddVersion(WsResource):
 
     def render_POST(self, txrequest):
-        eggf = BytesIO(_pop_required_param(txrequest.args, b'egg')[0])
-        if not zipfile.is_zipfile(eggf):
+        egg = _pop_required_param(txrequest.args, b'egg')[0]
+        if not zipfile.is_zipfile(BytesIO(egg)):
             return {"status": "error", "message": "egg is not a ZIP file (if using curl, use egg=@path not egg=path)"}
+        eggf = BytesIO(egg)
         args = native_stringify_dict(copy(txrequest.args), keys_only=False)
         project = _get_required_param(args, 'project')[0]
         version = _get_required_param(args, 'version')[0]