diff --git a/datetime_tz/__init__.py b/datetime_tz/__init__.py
index e939a56..8947c29 100644
--- a/datetime_tz/__init__.py
+++ b/datetime_tz/__init__.py
@@ -41,6 +41,7 @@
 import os.path
 import re
 import sys
+import struct
 import time
 import warnings
 import dateutil.parser
@@ -256,7 +257,11 @@ def _detect_timezone_etc_timezone():
 
 def _load_local_tzinfo():
   """Load zoneinfo from local disk."""
-  tzdir = os.environ.get("TZDIR", "/usr/share/zoneinfo/posix")
+  if os.path.exists("/usr/share/zoneinfo/posix"):
+    _tzdir = "/usr/share/zoneinfo/posix"
+  else:
+    _tzdir = "/usr/share/zoneinfo"
+  tzdir = os.environ.get("TZDIR", _tzdir)
 
   localtzdata = {}
   for dirpath, _, filenames in os.walk(tzdir):
@@ -264,9 +269,11 @@ def _load_local_tzinfo():
       filepath = os.path.join(dirpath, filename)
       name = os.path.relpath(filepath, tzdir)
 
-      f = open(filepath, "rb")
-      tzinfo = pytz.tzfile.build_tzinfo(name, f)
-      f.close()
+      with open(filepath, "rb") as f:
+        try:
+          tzinfo = pytz.tzfile.build_tzinfo(name, f)
+        except (AssertionError, struct.error):
+          continue
       localtzdata[name] = tzinfo
 
   return localtzdata
@@ -276,9 +283,8 @@ def _detect_timezone_etc_localtime():
   """Detect timezone based on /etc/localtime file."""
   matches = []
   if os.path.exists("/etc/localtime"):
-    f = open("/etc/localtime", "rb")
-    localtime = pytz.tzfile.build_tzinfo("/etc/localtime", f)
-    f.close()
+    with open("/etc/localtime", "rb") as f:
+      localtime = pytz.tzfile.build_tzinfo("/etc/localtime", f)
 
     # We want to match against the local database because /etc/localtime will
     # be copied from that. Once we have found a name for /etc/localtime, we can
diff --git a/tests.py b/tests.py
index b790bfd..1b0ba7e 100644
--- a/tests.py
+++ b/tests.py
@@ -86,6 +86,10 @@
 
 FMT = "%Y-%m-%d %H:%M:%S %Z%z"
 
+if sys.platform == "darwin":
+  TZDIR_POSIX = "/usr/share/zoneinfo"
+else:
+  TZDIR_POSIX = "/usr/share/zoneinfo/posix"
 
 # Older versions of pytz only have AmbiguousTimeError, while newer versions
 # throw NonExistentTimeError.
@@ -307,7 +311,7 @@ def os_path_exists_fake(filename, os_path_exists=os.path.exists):
     os_walk = os.walk
     def os_walk_fake(dirname, *args, **kw):
       if dirname in (
-          "/usr/share/zoneinfo/posix",
+          TZDIR_POSIX,
           ):
         return [
             (dirname, ["Etc", "Australia"], []),
@@ -323,13 +327,13 @@ def localtime_valid_fake(filename, *args, **kw):
         filename = os.path.join(os.path.dirname(__file__),
                                 localtime_file)
       if filename in (
-          "/usr/share/zoneinfo/posix/Australia/Melbourne",
-          "/usr/share/zoneinfo/posix/Australia/Sydney",
+          os.path.join(TZDIR_POSIX, "Australia/Melbourne"),
+          os.path.join(TZDIR_POSIX, "Australia/Sydney"),
           ):
         filename = test_zonedata_sydney
 
       if filename in (
-          "/usr/share/zoneinfo/posix/Etc/UTC",
+          os.path.join(TZDIR_POSIX, "Etc/UTC"),
           ):
         filename = os.path.join(os.path.dirname(__file__),
                                 "test_zonedata_utc")