diff --git a/humps/main.py b/humps/main.py
index 4e3844d..810c993 100644
--- a/humps/main.py
+++ b/humps/main.py
@@ -7,7 +7,7 @@
 
 ACRONYM_RE = re.compile(r"([A-Z\d]+)(?=[A-Z\d]|$)")
 PASCAL_RE = re.compile(r"([^\-_]+)")
-SPLIT_RE = re.compile(r"([\-_]*(?<=[^0-9])(?=[A-Z])[^A-Z]*[\-_]*)")
+SPLIT_RE = re.compile(r"([\-_]*(?<=[^0-9_])(?=[A-Z])[^A-Z]*[\-_]*)")
 UNDERSCORE_RE = re.compile(r"(?<=[^\-_])[\-_]+[^\-_]")
 
 
diff --git a/tests/test_humps.py b/tests/test_humps.py
index 0217228..61a56d7 100644
--- a/tests/test_humps.py
+++ b/tests/test_humps.py
@@ -24,6 +24,7 @@ def test_converting_strings():
         ("memMB", "mem_mb"),
         # Fixed issue #258
         ("B52Thing", "b52_thing"),
+        ("B2BThing", "b2b_thing"),
     ],
 )
 def test_camelized_acronyms(input_str, expected_output):