diff --git a/programs/mango-v4/src/state/orderbook/book.rs b/programs/mango-v4/src/state/orderbook/book.rs
index 2c254975f..79aa6d5e6 100644
--- a/programs/mango-v4/src/state/orderbook/book.rs
+++ b/programs/mango-v4/src/state/orderbook/book.rs
@@ -40,36 +40,6 @@ impl<'a> Orderbook<'a> {
         }
     }
 
-    pub fn best_price(&self, now_ts: u64, oracle_price_lots: i64, side: Side) -> Option<i64> {
-        Some(
-            self.bookside(side)
-                .iter_valid(now_ts, oracle_price_lots)
-                .next()?
-                .price_lots,
-        )
-    }
-
-    /// Walk up the book `quantity` units and return the price at that level. If `quantity` units
-    /// not on book, return None
-    pub fn impact_price(
-        &self,
-        side: Side,
-        quantity: i64,
-        now_ts: u64,
-        oracle_price_lots: i64,
-    ) -> Option<i64> {
-        let mut sum: i64 = 0;
-        let bookside = self.bookside(side);
-        let iter = bookside.iter_valid(now_ts, oracle_price_lots);
-        for order in iter {
-            cm!(sum += order.node.quantity);
-            if sum >= quantity {
-                return Some(order.price_lots);
-            }
-        }
-        None
-    }
-
     #[allow(clippy::too_many_arguments)]
     pub fn new_order(
         &mut self,
diff --git a/programs/mango-v4/src/state/orderbook/bookside.rs b/programs/mango-v4/src/state/orderbook/bookside.rs
index 961ac4950..05f54b64a 100644
--- a/programs/mango-v4/src/state/orderbook/bookside.rs
+++ b/programs/mango-v4/src/state/orderbook/bookside.rs
@@ -3,6 +3,7 @@ use num_enum::{IntoPrimitive, TryFromPrimitive};
 use static_assertions::const_assert_eq;
 
 use super::*;
+use crate::util::checked_math as cm;
 
 #[derive(
     Eq,
@@ -158,6 +159,28 @@ impl BookSide {
         }
         sum
     }
+
+    /// Return the price of the order closest to the spread
+    pub fn best_price(&self, now_ts: u64, oracle_price_lots: i64) -> Option<i64> {
+        Some(
+            self.iter_valid(now_ts, oracle_price_lots)
+                .next()?
+                .price_lots,
+        )
+    }
+
+    /// Walk up the book `quantity` units and return the price at that level. If `quantity` units
+    /// not on book, return None
+    pub fn impact_price(&self, quantity: i64, now_ts: u64, oracle_price_lots: i64) -> Option<i64> {
+        let mut sum: i64 = 0;
+        for order in self.iter_valid(now_ts, oracle_price_lots) {
+            cm!(sum += order.node.quantity);
+            if sum >= quantity {
+                return Some(order.price_lots);
+            }
+        }
+        None
+    }
 }
 
 #[cfg(test)]
diff --git a/programs/mango-v4/src/state/orderbook/order.rs b/programs/mango-v4/src/state/orderbook/order.rs
index c8b8f0a11..f97ebb631 100644
--- a/programs/mango-v4/src/state/orderbook/order.rs
+++ b/programs/mango-v4/src/state/orderbook/order.rs
@@ -99,8 +99,9 @@ impl Order {
         order_book: &Orderbook,
     ) -> i64 {
         if order_type == PostOrderType::PostOnlySlide {
-            if let Some(best_other_price) =
-                order_book.best_price(now_ts, oracle_price_lots, self.side.invert_side())
+            if let Some(best_other_price) = order_book
+                .bookside(self.side.invert_side())
+                .best_price(now_ts, oracle_price_lots)
             {
                 post_only_slide_limit(self.side, best_other_price, price_lots)
             } else {
diff --git a/programs/mango-v4/src/state/perp_market.rs b/programs/mango-v4/src/state/perp_market.rs
index c77c26604..cede555fb 100644
--- a/programs/mango-v4/src/state/perp_market.rs
+++ b/programs/mango-v4/src/state/perp_market.rs
@@ -221,8 +221,12 @@ impl PerpMarket {
         let oracle_price_lots = self.native_price_to_lot(oracle_price);
 
         // Get current book price & compare it to index price
-        let bid = book.impact_price(Side::Bid, self.impact_quantity, now_ts, oracle_price_lots);
-        let ask = book.impact_price(Side::Ask, self.impact_quantity, now_ts, oracle_price_lots);
+        let bid =
+            book.bookside(Side::Bid)
+                .impact_price(self.impact_quantity, now_ts, oracle_price_lots);
+        let ask =
+            book.bookside(Side::Ask)
+                .impact_price(self.impact_quantity, now_ts, oracle_price_lots);
 
         let diff_price = match (bid, ask) {
             (Some(bid), Some(ask)) => {