diff --git a/nbt.py b/nbt.py
index d4cc63f..59f7783 100644
--- a/nbt.py
+++ b/nbt.py
@@ -28,6 +28,8 @@ from contextlib import closing
 from numpy import array, zeros, uint8, fromstring
 TAGfmt = ">b"
 
+class NBTFormatError(RuntimeError): pass
+
 class TAG_Value(object):
     """Simple values. Subclasses override fmt to change the type and size. 
     Subclasses may set dataType instead of overriding setValue for automatic data type coercion"""
@@ -433,12 +435,12 @@ def load(filename="", buf=None):
     data = buf;
     #if buf != None: data = buf
     if not len(buf):
-        raise IOError, "Asked to load root tag of zero length"
+        raise NBTFormatError, "Asked to load root tag of zero length"
 
     data_cursor = 0;
     tag_type = data[data_cursor];
     if tag_type != 10:
-        raise IOError, 'Not an NBT file with a root TAG_Compound (found {0})'.format(tag_type);
+        raise NBTFormatError, 'Not an NBT file with a root TAG_Compound (found {0})'.format(tag_type);
     data_cursor += 1;
 
     data_cursor, tag = load_named(data, data_cursor, tag_type)