diff --git a/kcc/cbxarchive.py b/kcc/cbxarchive.py
index 216c1fa..6a7c598 100644
--- a/kcc/cbxarchive.py
+++ b/kcc/cbxarchive.py
@@ -27,6 +27,7 @@ from subprocess import STDOUT, PIPE
 from psutil import Popen
 from shutil import move, copy
 from . import rarfile
+from .shared import check7ZFile as is_7zfile
 
 
 class CBxArchive:
@@ -36,7 +37,7 @@ class CBxArchive:
             self.compressor = 'zip'
         elif rarfile.is_rarfile(origFileName):
             self.compressor = 'rar'
-        elif origFileName.endswith('.7z') or origFileName.endswith('.cb7'):
+        elif is_7zfile(origFileName):
             self.compressor = '7z'
         else:
             self.compressor = None
diff --git a/kcc/shared.py b/kcc/shared.py
index 418abf1..dbbdd44 100644
--- a/kcc/shared.py
+++ b/kcc/shared.py
@@ -52,3 +52,9 @@ def md5Checksum(filePath):
                 break
             m.update(data)
         return m.hexdigest()
+
+
+def check7ZFile(filePath):
+    with open(filePath, 'rb') as fh:
+        header = fh.read(6)
+    return header == b"7z\xbc\xaf'\x1c"
\ No newline at end of file