diff --git a/elements/space.py b/elements/space.py
index ec74cea..8e7e12a 100644
--- a/elements/space.py
+++ b/elements/space.py
@@ -1,3 +1,4 @@
+import ml_dtypes
 import numpy as np
 
 
@@ -13,7 +14,7 @@ def __init__(self, dtype, shape=(), low=None, high=None):
     self._high = self._infer_high(dtype, shape, low, high)
     self._shape = self._infer_shape(dtype, shape, self._low, self._high)
     self._discrete = (
-        np.issubdtype(self.dtype, np.integer) or self.dtype == bool)
+        issubdtype(self.dtype, np.integer) or self.dtype == bool)
     self._random = np.random.RandomState()
 
   @property
@@ -66,8 +67,8 @@ def __repr__(self):
 
   def __contains__(self, value):
     value = np.asarray(value)
-    if np.issubdtype(self.dtype, str):
-      return np.issubdtype(value.dtype, str)
+    if issubdtype(self.dtype, str):
+      return issubdtype(value.dtype, str)
     if value.shape != self.shape:
       return False
     if (value > self.high).any():
@@ -80,13 +81,13 @@ def __contains__(self, value):
 
   def sample(self):
     low, high = self.low, self.high
-    if np.issubdtype(self.dtype, np.floating):
-      low = np.maximum(np.ones(self.shape) * np.finfo(self.dtype).min, low)
-      high = np.minimum(np.ones(self.shape) * np.finfo(self.dtype).max, high)
+    if issubdtype(self.dtype, np.floating):
+      low = np.maximum(np.ones(self.shape) * ml_dtypes.finfo(self.dtype).min, low)
+      high = np.minimum(np.ones(self.shape) * ml_dtypes.finfo(self.dtype).max, high)
     return self._random.uniform(low, high, self.shape).astype(self.dtype)
 
   def _infer_low(self, dtype, shape, low, high):
-    if np.issubdtype(dtype, str):
+    if issubdtype(dtype, str):
       assert low is None, low
       return None
     if low is not None:
@@ -94,17 +95,17 @@ def _infer_low(self, dtype, shape, low, high):
         return np.broadcast_to(low, shape)
       except ValueError:
         raise ValueError(f'Cannot broadcast {low} to shape {shape}')
-    elif np.issubdtype(dtype, np.floating):
+    elif issubdtype(dtype, np.floating):
       return -np.inf * np.ones(shape)
-    elif np.issubdtype(dtype, np.integer):
+    elif issubdtype(dtype, np.integer):
       return np.iinfo(dtype).min * np.ones(shape, dtype)
-    elif np.issubdtype(dtype, bool):
+    elif issubdtype(dtype, bool):
       return np.zeros(shape, bool)
     else:
       raise ValueError('Cannot infer low bound from shape and dtype.')
 
   def _infer_high(self, dtype, shape, low, high):
-    if np.issubdtype(dtype, str):
+    if issubdtype(dtype, str):
       assert high is None, high
       return None
     if high is not None:
@@ -112,11 +113,11 @@ def _infer_high(self, dtype, shape, low, high):
         return np.broadcast_to(high, shape)
       except ValueError:
         raise ValueError(f'Cannot broadcast {high} to shape {shape}')
-    elif np.issubdtype(dtype, np.floating):
+    elif issubdtype(dtype, np.floating):
       return np.inf * np.ones(shape)
-    elif np.issubdtype(dtype, np.integer):
+    elif issubdtype(dtype, np.integer):
       return np.iinfo(dtype).max * np.ones(shape, dtype)
-    elif np.issubdtype(dtype, bool):
+    elif issubdtype(dtype, bool):
       return np.ones(shape, bool)
     else:
       raise ValueError('Cannot infer high bound from shape and dtype.')
@@ -130,3 +131,14 @@ def _infer_shape(self, dtype, shape, low, high):
       shape = (shape,)
     assert all(dim and dim > 0 for dim in shape), shape
     return tuple(shape)
+
+
+def issubdtype(a, b):
+  custom_float_dtypes = [getattr(ml_dtypes, name) for name in dir(ml_dtypes) if 'float' in name]
+  if a in custom_float_dtypes:
+    return b in {a, np.floating, np.inexact, np.number, np.generic}
+  if a in [ml_dtypes.int2, ml_dtypes.int4]:
+    return b in {a, np.signedinteger, np.integer, np.number, np.generic}
+  if a in [ml_dtypes.uint2, ml_dtypes.uint4]:
+    return b in {a, np.unsignedinteger, np.integer, np.number, np.generic}
+  return bool(np.issubdtype(a, b))
diff --git a/pyproject.toml b/pyproject.toml
index 7f2a75b..a25ae0a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -15,6 +15,7 @@ requires-python = ">=3.10"
 dependencies = [
   "google-auth",
   "google-cloud-storage",
+  "ml_dtypes",
   "numpy",
   "psutil",
   "ruamel.yaml",