diff --git a/src/stream/src/executor/over_window/over_partition.rs b/src/stream/src/executor/over_window/over_partition.rs
index e6d095e91e5c0..baac154593f7a 100644
--- a/src/stream/src/executor/over_window/over_partition.rs
+++ b/src/stream/src/executor/over_window/over_partition.rs
@@ -32,6 +32,7 @@ use risingwave_expr::window_function::{
 };
 use risingwave_storage::store::PrefetchOptions;
 use risingwave_storage::StateStore;
+use static_assertions::const_assert;
 
 use super::general::RowConverter;
 use crate::common::table::state_table::StateTable;
@@ -88,9 +89,11 @@ pub(super) fn shrink_partition_cache(
             let (sk_start, sk_end) = recently_accessed_range.into_inner();
             let (ck_start, ck_end) = (CacheKey::from(sk_start), CacheKey::from(sk_end));
 
+            // find the cursor just before `ck_start`
             let mut cursor = range_cache.inner().upper_bound(Bound::Excluded(&ck_start));
             for _ in 0..MAGIC_JITTER_PREVENTION {
                 if cursor.prev().is_none() {
+                    // already at the beginning
                     break;
                 }
             }
@@ -100,9 +103,11 @@ pub(super) fn shrink_partition_cache(
                 .unwrap_or_else(|| range_cache.first_key_value().unwrap().0)
                 .clone();
 
-            let mut cursor = range_cache.inner().lower_bound(Bound::Included(&ck_start));
+            // find the cursor just after `ck_end`
+            let mut cursor = range_cache.inner().lower_bound(Bound::Excluded(&ck_end));
             for _ in 0..MAGIC_JITTER_PREVENTION {
                 if cursor.next().is_none() {
+                    // already at the end
                     break;
                 }
             }
@@ -122,12 +127,18 @@ pub(super) fn shrink_partition_cache(
                 let (sk_start, _sk_end) = recently_accessed_range.into_inner();
                 let ck_start = CacheKey::from(sk_start);
 
-                let mut capacity_remain = MAGIC_CACHE_SIZE; // precision is not important here, code simplicity is first
+                let mut capacity_remain = MAGIC_CACHE_SIZE; // precision is not important here, code simplicity is the first
+                const_assert!(MAGIC_JITTER_PREVENTION < MAGIC_CACHE_SIZE);
 
-                let mut cursor = range_cache.inner().upper_bound(Bound::Excluded(&ck_start));
+                // find the cursor just before `ck_start`
+                let cursor_just_before_ck_start =
+                    range_cache.inner().upper_bound(Bound::Excluded(&ck_start));
+
+                let mut cursor = cursor_just_before_ck_start.clone();
                 // go back for at most `MAGIC_JITTER_PREVENTION` entries
                 for _ in 0..MAGIC_JITTER_PREVENTION {
                     if cursor.prev().is_none() {
+                        // already at the beginning
                         break;
                     }
                     capacity_remain -= 1;
@@ -138,10 +149,11 @@ pub(super) fn shrink_partition_cache(
                     .unwrap_or_else(|| range_cache.first_key_value().unwrap().0)
                     .clone();
 
-                let mut cursor = range_cache.inner().lower_bound(Bound::Included(&ck_start));
+                let mut cursor = cursor_just_before_ck_start;
                 // go forward for at most `capacity_remain` entries
                 for _ in 0..capacity_remain {
                     if cursor.next().is_none() {
+                        // already at the end
                         break;
                     }
                 }
@@ -162,12 +174,18 @@ pub(super) fn shrink_partition_cache(
                 let (_sk_start, sk_end) = recently_accessed_range.into_inner();
                 let ck_end = CacheKey::from(sk_end);
 
-                let mut capacity_remain = MAGIC_CACHE_SIZE; // precision is not important here, code simplicity is first
+                let mut capacity_remain = MAGIC_CACHE_SIZE; // precision is not important here, code simplicity is the first
+                const_assert!(MAGIC_JITTER_PREVENTION < MAGIC_CACHE_SIZE);
+
+                // find the cursor just after `ck_end`
+                let cursor_just_after_ck_end =
+                    range_cache.inner().lower_bound(Bound::Excluded(&ck_end));
 
-                let mut cursor = range_cache.inner().lower_bound(Bound::Excluded(&ck_end));
+                let mut cursor = cursor_just_after_ck_end.clone();
                 // go forward for at most `MAGIC_JITTER_PREVENTION` entries
                 for _ in 0..MAGIC_JITTER_PREVENTION {
                     if cursor.next().is_none() {
+                        // already at the end
                         break;
                     }
                     capacity_remain -= 1;
@@ -178,10 +196,11 @@ pub(super) fn shrink_partition_cache(
                     .unwrap_or_else(|| range_cache.last_key_value().unwrap().0)
                     .clone();
 
-                let mut cursor = range_cache.inner().upper_bound(Bound::Included(&ck_end));
+                let mut cursor = cursor_just_after_ck_end;
                 // go back for at most `capacity_remain` entries
                 for _ in 0..capacity_remain {
                     if cursor.prev().is_none() {
+                        // already at the beginning
                         break;
                     }
                 }