diff --git a/CHANGELOG.md b/CHANGELOG.md
index 75f355406d..5bdb61264a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -41,6 +41,7 @@
 - Fixed `input_note::remove_asset` succeeding when asked to remove an empty or malformed asset ID instead of reporting the asset as not found ([#3592](https://github.com/0xMiden/protocol/pull/3607)).
 - Faucet asset-callback procedure roots are now verified against the faucet's account code before dispatch, so a misconfigured callback root can no longer make an asset nontransferable ([#3612](https://github.com/0xMiden/protocol/pull/3612)).
 - [BREAKING] Enforced the limit of 1024 per asset delta op for added and removed account vault deltas inside and outside the tx kernel ([#3623](https://github.com/0xMiden/protocol/pull/3623)).
+- [BREAKING] Priced PSWAP fills against the note's initial offered asset rather than its remaining assets ([#3601](https://github.com/0xMiden/protocol/issues/3601)).
 - Fixed `AccountSchemaCommitment`'s `get_schema_commitment` returning above the 16-element stack depth ([#3645](https://github.com/0xMiden/protocol/pull/3645)).
 
 ## v0.16.0 (2026-08-17)
diff --git a/crates/miden-standards/asm/standards/notes/pswap.masm b/crates/miden-standards/asm/standards/notes/pswap.masm
index d460c28aba..e9315cb2a4 100644
--- a/crates/miden-standards/asm/standards/notes/pswap.masm
+++ b/crates/miden-standards/asm/standards/notes/pswap.masm
@@ -64,6 +64,10 @@ const PSWAP_CREATOR_PREFIX_ITEM = STORAGE_PTR + 6
 const CALC_FILL_AMOUNT = 0
 const CALC_FILL_REFERENCE = 1
 
+# Procedure locals of load_offered_asset
+const OFFERED_REMAINING_ASSET_PTR = 0
+const OFFERED_INITIAL_ASSET_PTR = 8
+
 # create_p2id_note locals
 const P2ID_NOTE_IDX = 0
 const P2ID_REQUESTED_FAUCET_SUFFIX = 1
@@ -100,6 +104,7 @@ const PARENT_ATTACHMENT_DEPTH_OFFSET = 2
 
 const ERR_PSWAP_WRONG_NUMBER_OF_STORAGE_ITEMS="PSWAP script expects exactly 7 note storage items"
 const ERR_PSWAP_WRONG_NUMBER_OF_ASSETS="PSWAP script requires exactly one note asset"
+const ERR_PSWAP_OFFERED_ASSET_ALTERED="PSWAP offered asset differs from the asset the note was created with"
 const ERR_PSWAP_FILL_SUM_OVERFLOW="PSWAP account_fill + note_fill overflows u64"
 const ERR_PSWAP_NOT_VALID_ASSET_AMOUNT="PSWAP computed amount exceeds max fungible asset amount"
 const ERR_PSWAP_PAYOUT_OVERFLOW="PSWAP payout quotient does not fit in u64"
@@ -449,23 +454,43 @@ proc is_consumer_creator
     # => [is_creator]
 end
 
-#! Loads the offered asset from the active note and validates there is exactly one asset.
+#! Loads the note's single offered asset, asserting it equals the amount the note was created with.
 #!
 #! Inputs: []
 #! Outputs: [ASSET_ID, ASSET_VALUE]
 #!
-@locals(8)
+#! Panics if:
+#! - the note does not carry exactly one remaining asset.
+#! - the note was not created with exactly one asset.
+#! - the remaining offered asset differs from the asset the note was created with.
+#!
+@locals(16)
 proc load_offered_asset
-    locaddr.0 exec.active_note::remove_all_assets
+    locaddr.OFFERED_REMAINING_ASSET_PTR exec.active_note::remove_all_assets
     # => [num_assets]
 
     push.1 eq assert.err=ERR_PSWAP_WRONG_NUMBER_OF_ASSETS
     # => []
 
-    locaddr.0
-    # => [dest_ptr]
+    # initial assets are unaffected by removals; require exactly one
+    locaddr.OFFERED_INITIAL_ASSET_PTR exec.active_note::get_initial_assets
+    # => [num_initial_assets]
+
+    eq.1 assert.err=ERR_PSWAP_OFFERED_ASSET_ALTERED
+    # => []
+
+    locaddr.OFFERED_REMAINING_ASSET_PTR exec.asset::load
+    # => [ASSET_ID, ASSET_VALUE]
+
+    locaddr.OFFERED_INITIAL_ASSET_PTR exec.asset::load
+    # => [INITIAL_ASSET_ID, INITIAL_ASSET_VALUE, ASSET_ID, ASSET_VALUE]
+
+    # the remaining offered asset must equal the initial one
+    movupw.2 assert_eqw.err=ERR_PSWAP_OFFERED_ASSET_ALTERED
+    assert_eqw.err=ERR_PSWAP_OFFERED_ASSET_ALTERED
+    # => []
 
-    exec.asset::load
+    locaddr.OFFERED_REMAINING_ASSET_PTR exec.asset::load
     # => [ASSET_ID, ASSET_VALUE]
 end
 
@@ -808,6 +833,8 @@ end
 #! Panics if:
 #! - the number of note storage items is not `NUM_STORAGE_ITEMS`.
 #! - the note does not hold exactly one offered asset at consumption time.
+#! - the offered asset remaining in the note differs from the asset the note was created with (i.e.
+#!   it was partially removed before the script ran).
 #! - the total fill (account_fill + note_fill) overflows u64 or exceeds the max asset amount.
 #! - the account does not expose `receive_asset` / `move_asset_to_note`.
 @note_script
diff --git a/crates/miden-standards/src/note/pswap.rs b/crates/miden-standards/src/note/pswap.rs
index ac360be6c9..0074e820b8 100644
--- a/crates/miden-standards/src/note/pswap.rs
+++ b/crates/miden-standards/src/note/pswap.rs
@@ -267,6 +267,8 @@ impl From<PswapNoteAttachment> for NoteAttachment {
 /// `[0, 0, 0, 0]`, triggering a full fill). To route a PSWAP note to a network account,
 /// set the `attachment` to a [`NetworkAccountTarget`](crate::note::NetworkAccountTarget)
 /// via the builder.
+///
+/// Fills are priced against the note's initial offered asset.
 #[derive(Debug, Clone, bon::Builder)]
 #[builder(finish_fn(vis = "", name = build_internal))]
 pub struct PswapNote {
diff --git a/crates/miden-testing/tests/scripts/pswap.rs b/crates/miden-testing/tests/scripts/pswap.rs
index f158f2d81a..35d2fe16aa 100644
--- a/crates/miden-testing/tests/scripts/pswap.rs
+++ b/crates/miden-testing/tests/scripts/pswap.rs
@@ -1,7 +1,14 @@
 use std::collections::BTreeMap;
 
 use miden_protocol::account::auth::AuthScheme;
-use miden_protocol::account::{Account, AccountId, AccountType, AccountVaultPatch};
+use miden_protocol::account::component::AccountComponentMetadata;
+use miden_protocol::account::{
+    Account,
+    AccountComponent,
+    AccountId,
+    AccountType,
+    AccountVaultPatch,
+};
 use miden_protocol::asset::{Asset, AssetAmount, AssetId, FungibleAsset};
 use miden_protocol::crypto::rand::{FeltRng, RandomCoin};
 use miden_protocol::errors::MasmError;
@@ -10,14 +17,22 @@ use miden_protocol::testing::account_id::AccountIdBuilder;
 use miden_protocol::transaction::{RawOutputNote, RawOutputNotes};
 use miden_protocol::{Felt, ONE, Word, ZERO};
 use miden_standards::account::wallets::BasicWallet;
+use miden_standards::code_builder::CodeBuilder;
 use miden_standards::errors::standards::{
     ERR_PSWAP_FILL_BELOW_MINIMUM,
     ERR_PSWAP_FILL_SUM_OVERFLOW,
     ERR_PSWAP_NOT_VALID_ASSET_AMOUNT,
+    ERR_PSWAP_OFFERED_ASSET_ALTERED,
 };
 use miden_standards::note::{PswapNote, PswapNoteAttachment, PswapNoteStorage};
 use miden_standards::testing::note::NoteBuilder;
-use miden_testing::{Auth, MockChain, MockChainBuilder, assert_transaction_executor_error};
+use miden_testing::{
+    AccountState,
+    Auth,
+    MockChain,
+    MockChainBuilder,
+    assert_transaction_executor_error,
+};
 use rand::SeedableRng;
 use rand::rngs::SmallRng;
 use rstest::rstest;
@@ -2072,3 +2087,131 @@ fn pswap_parse_inputs_roundtrip() {
     // Verify requested amount from value word
     assert_eq!(parsed.min_requested_amount(), 25, "Requested amount should be 25");
 }
+
+/// Regression test for the offered-asset drain (issue #3601, PSWAP leg).
+///
+/// A PSWAP note offers 1000 USDC for a minimum of 100 ETH. The consuming account exposes an
+/// `@account_procedure` performing indexed input-note asset removal (`input_note::remove_asset`),
+/// permitted only from the native-account context. An earlier helper input note (index 0) calls it
+/// to drain 900 USDC out of the PSWAP note (index 1) before the PSWAP script runs. A partial fill
+/// must then abort with `ERR_PSWAP_OFFERED_ASSET_ALTERED`.
+#[tokio::test]
+async fn pswap_note_offered_asset_drain_is_rejected_test() -> anyhow::Result<()> {
+    let mut builder = MockChain::builder();
+
+    let usdc_faucet = builder.add_existing_basic_faucet(BASIC_AUTH, "USDC", 10_000, Some(1_000))?;
+    let eth_faucet = builder.add_existing_basic_faucet(BASIC_AUTH, "ETH", 10_000, Some(100))?;
+
+    let alice = AccountIdBuilder::new().build_with_seed([1; 32]);
+
+    // A component that drains a specified asset from an input note by index into the account's own
+    // vault.
+    let drain_component = AccountComponent::new(
+        CodeBuilder::default().compile_component_code(
+            "attacker_account",
+            "
+            use miden::protocol::asset
+            use miden::protocol::input_note
+            use miden::protocol::native_account
+
+            #! Removes the given asset from the input note at `note_index` and credits it to this
+            #! account's vault.
+            #!
+            #! Inputs:  [ASSET_ID, ASSET_VALUE, note_index, pad(7)]
+            #! Outputs: [pad(16)]
+            @account_procedure
+            @locals(8)
+            pub proc drain_note_asset
+                # keep a copy of the asset so it can be credited to the vault after removal
+                dupw.1 dupw.1 locaddr.0 exec.asset::store
+                # => [ASSET_ID, ASSET_VALUE, note_index, pad(7)]
+
+                exec.input_note::remove_asset
+                # => [FINAL_ASSET_VALUE, pad(7)]
+
+                dropw
+                # => [pad(7)]
+
+                # credit the drained asset to the consuming account's vault
+                locaddr.0 exec.asset::load exec.native_account::add_asset dropw
+                # => [pad(7)]
+            end
+            ",
+        )?,
+        Vec::new(),
+        AccountComponentMetadata::mock("attacker_account"),
+    )?;
+
+    let consumer = builder.add_account_from_builder(
+        BASIC_AUTH,
+        Account::builder([9; 32])
+            .account_type(AccountType::Public)
+            .with_component(BasicWallet)
+            .with_component(drain_component.clone())
+            .with_assets([FungibleAsset::new(eth_faucet.id(), 100)?.into()]),
+        AccountState::Exists,
+    )?;
+
+    // Alice's PSWAP note offers 1000 USDC for a minimum of 100 ETH.
+    let offered_asset = FungibleAsset::new(usdc_faucet.id(), 1_000)?;
+    let min_requested_asset = FungibleAsset::new(eth_faucet.id(), 100)?;
+    let (_, pswap_note) = build_pswap_note(
+        &mut builder,
+        alice,
+        offered_asset,
+        min_requested_asset,
+        NoteType::Public,
+    )?;
+
+    // Helper note (input note index 0) that drains 900 of the 1000 offered USDC out of the PSWAP
+    // note (input note index 1) via the consuming account's procedure.
+    let drained = FungibleAsset::new(usdc_faucet.id(), 900)?;
+    let pswap_input_note_index = 1u8;
+    let helper_code = format!(
+        r#"
+        use miden::core::sys
+
+        @note_script
+        pub proc main
+            # Drain the offered asset from the PSWAP note by index, via the native account's
+            # procedure, before the PSWAP script gets to consume its own remaining assets.
+            push.0.0.0.0 push.0.0.0
+            push.{pswap_input_note_index}
+            push.{asset_value}
+            push.{asset_id}
+            call.::attacker_account::drain_note_asset
+            exec.sys::truncate_stack
+        end
+    "#,
+        asset_value = drained.to_value_word(),
+        asset_id = drained.to_id_word(),
+    );
+    let helper_script = CodeBuilder::with_mock_packages()
+        .with_dynamically_linked_package(drain_component.component_code())?
+        .compile_note_script(helper_code)?;
+    let helper_note = NoteBuilder::new(alice, RandomCoin::new(Word::from([7, 7, 7, 7u32])))
+        .note_type(NoteType::Public)
+        .script(helper_script)
+        .build()?;
+    // Commit the helper note so it can be consumed as an authenticated input note (index 0).
+    let helper_note_id = helper_note.id();
+    builder.add_output_note(RawOutputNote::Full(helper_note));
+
+    let mock_chain = builder.build()?;
+
+    // A 50-of-100 ETH partial fill, which exercises the remainder-note pricing path.
+    let mut note_args_map = BTreeMap::new();
+    note_args_map.insert(pswap_note.id(), PswapNote::create_args(50, 0)?);
+
+    let result = mock_chain
+        .build_transaction(consumer.id())
+        .authenticated_input_notes([helper_note_id, pswap_note.id()])
+        .extend_note_args(note_args_map)
+        .build()?
+        .execute()
+        .await;
+
+    assert_transaction_executor_error!(result, ERR_PSWAP_OFFERED_ASSET_ALTERED);
+
+    Ok(())
+}