diff --git a/blockcypher/utils.py b/blockcypher/utils.py
index 87a2c0c..2dcab74 100644
--- a/blockcypher/utils.py
+++ b/blockcypher/utils.py
@@ -11,7 +11,7 @@
 from collections import OrderedDict
 from hashlib import sha256
 
-HEX_CHARS_RE = re.compile('^[0-9a-f]*$')
+HEX_CHARS_RE = re.compile('^[0-9a-f]*$', re.IGNORECASE)
 
 
 def format_output(num, output_type):