diff --git a/atrcopy/__init__.py b/atrcopy/__init__.py
index c1aa079..28e416a 100644
--- a/atrcopy/__init__.py
+++ b/atrcopy/__init__.py
@@ -253,7 +253,7 @@ def assemble(image, source_files, data_files, obj_files, run_addr=""):
 def boot_image(image_name, source_files, data_files, obj_files, run_addr=""):
     try:
         image_cls = parsers_for_filename(image_name)[0]
-    except InvalidDiskImage, e:
+    except InvalidDiskImage as e:
         print("%s: %s" % (image_name, e))
         return None
     segments, run_addr = assemble_segments(source_files, data_files, obj_files, run_addr)
@@ -356,7 +356,7 @@ def create_image(template, name):
 
     try:
         data, inf = get_template_data(template)
-    except InvalidDiskImage, e:
+    except InvalidDiskImage as e:
         info = get_template_info()
         print("Error: %s\n\n%s" % (e, info))
         return
@@ -548,6 +548,8 @@ def run():
                 args.append('list')
     else:
         disk_image_name = None
+        parser.print_help()
+        sys.exit(1)
 
     # print "parsing: %s" % str(args)
     options = parser.parse_args(args)
diff --git a/atrcopy/ataridos.py b/atrcopy/ataridos.py
index 1a3acad..a1caa69 100644
--- a/atrcopy/ataridos.py
+++ b/atrcopy/ataridos.py
@@ -350,7 +350,7 @@ class AtrHeader(BaseHeader):
         if len(bytes) == 16:
             values = bytes.view(dtype=self.format)[0]
             if values[0] != 0x296:
-                raise InvalidAtrHeader
+                raise InvalidAtrHeader("no ATR header magic value")
             self.image_size = (int(values[3]) * 256 * 256 + int(values[1])) * 16
             self.sector_size = int(values[2])
             self.crc = int(values[4])
@@ -358,7 +358,7 @@ class AtrHeader(BaseHeader):
             self.flags = int(values[6])
             self.header_offset = 16
         else:
-            raise InvalidAtrHeader
+            raise InvalidAtrHeader("incorrect AHC header size of %d" % len(bytes))
 
     def __str__(self):
         return "%s Disk Image (size=%d (%dx%dB), crc=%d flags=%d unused=%d)" % (self.file_format, self.image_size, self.max_sectors, self.sector_size, self.crc, self.flags, self.unused)
@@ -743,7 +743,6 @@ class AtariDiskImage(BootDiskImage):
         return "%s Unidentified Contents" % (self.header)
 
     def check_size(self):
-        print self.header
         if self.header is None:
             raise ("Not a known Atari disk image format")