diff --git a/opengsq/responses/source/environment.py b/opengsq/responses/source/environment.py
index 78fc6c2..53bb20d 100644
--- a/opengsq/responses/source/environment.py
+++ b/opengsq/responses/source/environment.py
@@ -17,4 +17,18 @@ class Environment(IntEnum):
 
     @staticmethod
     def parse(byte: int):
-        return Environment(ord(chr(byte).lower()))
+        """
+        Parses the given byte to an Environment value. If the byte does not correspond to a valid
+        Environment value, it defaults to Environment.Mac.
+
+        Args:
+            byte (int): The byte to parse.
+
+        Returns:
+            Environment: The corresponding Environment value, or Environment.Mac if the byte is not valid.
+        """
+        try:
+            return Environment(ord(chr(byte).lower()))
+        except ValueError:
+            # 'm' or 'o' for Mac (the code changed after L4D1)
+            return Environment.Mac
diff --git a/opengsq/responses/source/server_type.py b/opengsq/responses/source/server_type.py
index 115a17b..249c69e 100644
--- a/opengsq/responses/source/server_type.py
+++ b/opengsq/responses/source/server_type.py
@@ -17,4 +17,14 @@ class ServerType(IntEnum):
 
     @staticmethod
     def parse(byte: int):
+        """
+        Parses the given byte to a ServerType value. If the byte does not correspond to a valid
+        ServerType value, a ValueError is raised.
+
+        Args:
+            byte (int): The byte to parse.
+
+        Returns:
+            ServerType: The corresponding ServerType value.
+        """
         return ServerType(ord(chr(byte).lower()))