diff --git a/parsedmarc/utils.py b/parsedmarc/utils.py
index 4bea71a..b86cefc 100644
--- a/parsedmarc/utils.py
+++ b/parsedmarc/utils.py
@@ -325,9 +325,18 @@ def get_filename_safe_string(string):
     return string
 
 
-def is_outlook_msg(suspect_bytes):
-    """Checks if the given content is a Outlook msg OLE file"""
-    return suspect_bytes.startswith(b"\xD0\xCF\x11\xE0\xA1\xB1\x1A\xE1")
+def is_outlook_msg(content):
+    """
+    Checks if the given content is a Outlook msg OLE file
+
+    Args:
+        content: Content to check
+
+    Returns:
+        bool: A flag the indicates if a file is a Outlook MSG file
+    """
+    return type(content) == bytes and content.startswith(
+        b"\xD0\xCF\x11\xE0\xA1\xB1\x1A\xE1")
 
 
 def convert_outlook_msg(msg_bytes):