diff --git a/Cargo.lock b/Cargo.lock
index 7fb52e90..1410f125 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -599,7 +599,7 @@ dependencies = [
 [[package]]
 name = "rgb-core"
 version = "0.11.0-beta.1"
-source = "git+https://github.com/RGB-WG/rgb-core?branch=v0.11#8abc864deb3d907afa2644aed11f9a739c79c565"
+source = "git+https://github.com/RGB-WG/rgb-core?branch=v0.11#d80b3f516994d005578c010d22362d9a25783d23"
 dependencies = [
  "aluvm",
  "amplify",
diff --git a/src/interface/builder.rs b/src/interface/builder.rs
index 5e42c587..72136af7 100644
--- a/src/interface/builder.rs
+++ b/src/interface/builder.rs
@@ -64,9 +64,9 @@ pub enum BuilderError {
     /// state `{0}` provided to the builder has invalid name.
     InvalidState(AssignmentType),
 
-    /// can't add asset of type `{0}`: you need to register the type with asset
-    /// type firtst using `add_asset_tag` method.
-    AssetTagUnknown(AssignmentType),
+    /// asset tag for the state `{0}` must be added before any fungible state of
+    /// the same type.
+    AssetTagSet(AssignmentType),
 
     /// interface doesn't specifies default operation name, thus an explicit
     /// operation type must be provided with `set_operation_type` method.
@@ -431,6 +431,10 @@ impl<Seal: ExposedSeal> OperationBuilder<Seal> {
             .assignments_type(&name, ty)
             .ok_or(BuilderError::AssignmentNotFound(name))?;
 
+        if self.fungible.contains_key(&type_id) {
+            return Err(BuilderError::AssetTagSet(type_id));
+        }
+
         self.asset_tags.insert(type_id, asset_tag)?;
         Ok(self)
     }
@@ -481,10 +485,17 @@ impl<Seal: ExposedSeal> OperationBuilder<Seal> {
             .assignments_type(&name, ty)
             .ok_or(BuilderError::AssignmentNotFound(name))?;
 
-        let tag = *self
-            .asset_tags
-            .get(&type_id)
-            .ok_or(BuilderError::AssetTagUnknown(type_id))?;
+        let tag = match self.asset_tags.get(&type_id) {
+            Some(asset_tag) => *asset_tag,
+            None => {
+                let asset_tag = AssetTag::new_random(
+                    format!("{}/{}", self.schema.schema_id(), self.iface.iface_id()),
+                    type_id,
+                );
+                self.asset_tags.insert(type_id, asset_tag)?;
+                asset_tag
+            }
+        };
 
         let state = RevealedValue::new_random_blinding(value, tag);
 
diff --git a/src/interface/mod.rs b/src/interface/mod.rs
index 2ac4afc5..8ec4554a 100644
--- a/src/interface/mod.rs
+++ b/src/interface/mod.rs
@@ -32,7 +32,6 @@ pub mod rgb21;
 pub mod rgb25;
 mod suppl;
 
-pub use asset_tag_ext::AssetTagExt;
 pub use builder::{BuilderError, ContractBuilder, TransitionBuilder};
 pub use contract::{
     AllocationWitness, ContractIface, FilterExclude, FilterIncludeAll, FungibleAllocation,
@@ -63,30 +62,3 @@ pub enum VerNo {
     #[display("v1")]
     V1 = 0,
 }
-
-// TODO: Move to RGB Core
-mod asset_tag_ext {
-    use std::time::SystemTime;
-
-    use amplify::confinement::U8;
-    use bp::secp256k1::rand::{thread_rng, RngCore};
-    use commit_verify::{DigestExt, Sha256};
-    use rgb::{AssetTag, AssignmentType};
-
-    pub trait AssetTagExt: Sized {
-        fn new_random(contract_domain: impl AsRef<str>, assignment_type: AssignmentType) -> Self;
-    }
-
-    impl AssetTagExt for AssetTag {
-        fn new_random(contract_domain: impl AsRef<str>, assignment_type: AssignmentType) -> Self {
-            let rand = thread_rng().next_u64();
-            let timestamp = SystemTime::now().elapsed().expect("system time error");
-            let mut hasher = Sha256::default();
-            hasher.input_with_len::<U8>(contract_domain.as_ref().as_bytes());
-            hasher.input_raw(&assignment_type.to_le_bytes());
-            hasher.input_raw(&timestamp.as_nanos().to_le_bytes());
-            hasher.input_raw(&rand.to_le_bytes());
-            AssetTag::from(hasher.finish())
-        }
-    }
-}