diff --git a/ceos_alos2/hierarchy.py b/ceos_alos2/hierarchy.py
index aa5b596..ac70063 100644
--- a/ceos_alos2/hierarchy.py
+++ b/ceos_alos2/hierarchy.py
@@ -11,6 +11,23 @@
 from ceos_alos2.array import Array
 
 
+def _infer_dtype(data):
+    # If obj is a list or lacks a dtype, convert to numpy array
+    if not data:
+        return None
+    first = data[0]
+    if isinstance(first, int):
+        return np.int64  # consistent across platforms
+    elif isinstance(first, float):
+        return np.float64
+    elif isinstance(first, str):
+        # Use fixed-length string to avoid object dtype
+        # CEOS strings are usually ASCII, e.g., 'ALOS-2''
+        return np.dtypes.StrDType
+    else:
+        return None  # let numpy infer
+
+
 @dataclass(frozen=True)
 class Variable:
     dims: str | list[str]
@@ -21,6 +38,9 @@ def __post_init__(self):
         if isinstance(self.dims, str):
             # normalize, need the hack
             super().__setattr__("dims", [self.dims])
+        if isinstance(self.data, list):
+            # Infer dtype more carefully, or force appropriate dtype
+            super().__setattr__("data", np.array(self.data, dtype=_infer_dtype(self.data)))
 
     def __eq__(self, other):
         if not isinstance(other, Variable):