diff --git a/src/resfo/_formatted/read.py b/src/resfo/_formatted/read.py
index 20448f9..81a4b4a 100644
--- a/src/resfo/_formatted/read.py
+++ b/src/resfo/_formatted/read.py
@@ -21,7 +21,7 @@ class FormattedArray(ResArray):
     An array entry in an formatted res file.
     """
 
-    def __init__(self, stream):
+    def __init__(self, stream, keys_as_bytes=False):
         self.start = stream.tell()
         self.stream = stream
 
@@ -30,6 +30,7 @@ def __init__(self, stream):
         self._type = None
         self._data_start = None
         self._array = None
+        self._keys_as_bytes = keys_as_bytes
 
         self._is_eof = False
 
@@ -107,6 +108,8 @@ def _read_number(self):
 
     def _read_keyword(self):
         self._keyword = self._read_quote_separated()
+        if self._keys_as_bytes:
+            self._keyword = self._keyword.encode("ascii")
 
     def _read_type(self):
         self._type = self._read_quote_separated().encode("ascii")
diff --git a/src/resfo/_unformatted/read.py b/src/resfo/_unformatted/read.py
index 21db765..426e91f 100644
--- a/src/resfo/_unformatted/read.py
+++ b/src/resfo/_unformatted/read.py
@@ -1,4 +1,5 @@
 import io
+from abc import abstractmethod
 
 import numpy as np
 import resfo.types as res_types
@@ -8,7 +9,7 @@
 from resfo.errors import ResfoParsingError
 
 
-class UnformattedResArray(ResArray):
+class _UnformattedResArray(ResArray):
     """
     An array entry in a unformatted res file.
     """
@@ -77,14 +78,9 @@ def _read_record_marker(self, expected_value):
                 f"Unexpected size of record {value} ({value.to_bytes(4, byteorder='big', signed=True)})"
             )
 
+    @abstractmethod
     def _read_keyword(self):
-        """
-        With stream.peek() at the start of the keyword, reads
-        it into self._keyword
-        """
-        self._keyword = self.stream.read(8).decode("ascii")
-        if not self._keyword or len(self._keyword) < 8:
-            raise ResfoParsingError("Reached end-of-file while reading keyword")
+        pass
 
     def _read_type(self):
         """
@@ -153,3 +149,33 @@ def _read(self):
 
         self._data_start = self.stream.tell()
         self.stream.seek(bytes_to_skip, io.SEEK_CUR)
+
+
+class UnformattedResArray(_UnformattedResArray):
+    """
+    An array entry in a unformatted res file.
+    """
+
+    def _read_keyword(self):
+        """
+        With stream.peek() at the start of the keyword, reads
+        it into self._keyword
+        """
+        self._keyword = self.stream.read(8).decode("ascii")
+        if not self._keyword or len(self._keyword) < 8:
+            raise ResfoParsingError("Reached end-of-file while reading keyword")
+
+
+class UnformattedResArrayBytes(_UnformattedResArray):
+    """
+    An array entry in a unformatted res file.
+    """
+
+    def _read_keyword(self):
+        """
+        With stream.peek() at the start of the keyword, reads
+        it into self._keyword
+        """
+        self._keyword = self.stream.read(8)
+        if not self._keyword or len(self._keyword) < 8:
+            raise ResfoParsingError("Reached end-of-file while reading keyword")
diff --git a/src/resfo/array_entry.py b/src/resfo/array_entry.py
index fd85897..70cc994 100644
--- a/src/resfo/array_entry.py
+++ b/src/resfo/array_entry.py
@@ -108,18 +108,18 @@ def _read(self):
         pass
 
     @classmethod
-    def parse(cls, stream):
+    def parse(cls, stream, *args, **kwargs):
         """
         Parse an res file from the given opened file handle.
 
         Is a generator of ResArrays
         """
-        record = cls(stream)
+        record = cls(stream, *args, **kwargs)
 
         record._read()
 
         while not record._is_eof:
-            new_record = cls(stream)
+            new_record = cls(stream, *args, **kwargs)
             yield record
             new_record._read()
             record = new_record
diff --git a/src/resfo/read.py b/src/resfo/read.py
index 757b07e..46b2f34 100644
--- a/src/resfo/read.py
+++ b/src/resfo/read.py
@@ -1,7 +1,7 @@
 from typing import TYPE_CHECKING, Iterator, List, Optional, Tuple
 
 from resfo._formatted.read import FormattedArray
-from resfo._unformatted.read import UnformattedResArray
+from resfo._unformatted.read import UnformattedResArray, UnformattedResArrayBytes
 from resfo.array_entry import ResArray
 from resfo.format import Format, check_correct_mode, get_stream, guess_format
 
@@ -20,7 +20,9 @@ def read(*args, **kwargs) -> List[Tuple[str, "ReadArrayValue"]]:
     ]
 
 
-def lazy_read(filelike, fileformat: Optional[Format] = None) -> Iterator[ResArray]:
+def lazy_read(
+    filelike, fileformat: Optional[Format] = None, keys_as_bytes: bool = False
+) -> Iterator[ResArray]:
     """
     Reads the contents of an res file and generates the entries
     of that file. Each entry has a entry.read_keyword() and
@@ -42,6 +44,10 @@ def lazy_read(filelike, fileformat: Optional[Format] = None) -> Iterator[ResArra
     :param fileformat: Either resfo.Format.FORMATTED for ascii
         format, resfo.Format.UNFORMATTED for binary formatted files
         or None for guess.
+    :param keys_as_bytes: If fileformat=resf.Format.FORMATTED is given,
+        it is possible to request that the bytes of the keyword is given
+        undecoded. This is somewhat faster so can be useful for
+        files with many keywords.
 
     :raises resfo.ResfoParsingError: If the file is not a valid
         res file.
@@ -62,9 +68,12 @@ def lazy_read(filelike, fileformat: Optional[Format] = None) -> Iterator[ResArra
 
     try:
         if fileformat == Format.FORMATTED:
-            yield from FormattedArray.parse(stream)
+            yield from FormattedArray.parse(stream, keys_as_bytes=keys_as_bytes)
         else:
-            yield from UnformattedResArray.parse(stream)
+            if keys_as_bytes:
+                yield from UnformattedResArrayBytes.parse(stream)
+            else:
+                yield from UnformattedResArray.parse(stream)
     finally:
         if didopen:
             stream.close()