diff --git a/vortex-dtype/src/dtype.rs b/vortex-dtype/src/dtype.rs
index 6bde6e1b472..c103ae26221 100644
--- a/vortex-dtype/src/dtype.rs
+++ b/vortex-dtype/src/dtype.rs
@@ -110,7 +110,9 @@ impl DType {
                         .all(|(l, r)| l.eq_ignore_nullability(&r)))
             }
             (Struct(..), _) => false,
-            (Extension(lhs_extdtype), Extension(rhs_extdtype)) => lhs_extdtype == rhs_extdtype,
+            (Extension(lhs_extdtype), Extension(rhs_extdtype)) => {
+                lhs_extdtype.as_ref().eq_ignore_nullability(rhs_extdtype)
+            }
             (Extension(_), _) => false,
         }
     }
diff --git a/vortex-dtype/src/extension.rs b/vortex-dtype/src/extension.rs
index 305b3dff4df..a02475683f4 100644
--- a/vortex-dtype/src/extension.rs
+++ b/vortex-dtype/src/extension.rs
@@ -58,7 +58,7 @@ impl From<&[u8]> for ExtMetadata {
 }
 
 /// A type descriptor for an extension type
-#[derive(Debug, Clone, PartialOrd, Eq)]
+#[derive(Debug, Clone, PartialOrd, PartialEq, Eq, Hash)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct ExtDType {
     id: ExtID,
@@ -66,18 +66,6 @@ pub struct ExtDType {
     metadata: Option<ExtMetadata>,
 }
 
-impl PartialEq for ExtDType {
-    fn eq(&self, other: &Self) -> bool {
-        self.id == other.id
-    }
-}
-
-impl std::hash::Hash for ExtDType {
-    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
-        self.id.hash(state);
-    }
-}
-
 impl ExtDType {
     /// Creates a new `ExtDType`.
     ///
@@ -148,4 +136,13 @@ impl ExtDType {
     pub fn metadata(&self) -> Option<&ExtMetadata> {
         self.metadata.as_ref()
     }
+
+    /// Check if `self` and `other` are equal, ignoring the storage nullability
+    pub fn eq_ignore_nullability(&self, other: &Self) -> bool {
+        self.id() == other.id()
+            && self.metadata() == other.metadata()
+            && self
+                .storage_dtype()
+                .eq_ignore_nullability(other.storage_dtype())
+    }
 }