diff --git a/src/xtgeo/grid3d/_ecl_logi_head.py b/src/xtgeo/grid3d/_ecl_logi_head.py
index 3b99627f8..b4ce67a23 100644
--- a/src/xtgeo/grid3d/_ecl_logi_head.py
+++ b/src/xtgeo/grid3d/_ecl_logi_head.py
@@ -5,7 +5,7 @@
 from ._ecl_output_file import Simulator
 
 
-def lookup_optional_code(values, index):
+def lookup_optional_code(values: list[bool], index: int) -> bool | None:
     if len(values) <= index:
         return None
     return values[index]
@@ -54,7 +54,7 @@ class LogiHead:
     coal_bed_methane: bool | None = None
 
     @classmethod
-    def from_file_values(cls, values: list[bool], simulator: Simulator):
+    def from_file_values(cls, values: list[bool], simulator: Simulator) -> LogiHead:
         """Construct a LogiHead from the array following the LOGIHEAD keyword
         Args:
             values: The iterable of boolean values following the LOGIHEAD keyword