diff --git a/Cargo.lock b/Cargo.lock
index 470f9d2..80f3a37 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -155,12 +155,6 @@ version = "0.3.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0cc23270f6e1808e30a928bdc84dea0b9b4136a8bc82338574f23baf47bbd280"
 
-[[package]]
-name = "hashlru"
-version = "0.11.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d2c782df656366ccb42fbbac7c7c180535a43d906a138ffb491ec3ed56a239ab"
-
 [[package]]
 name = "icmp-socket2"
 version = "0.4.2"
@@ -426,7 +420,6 @@ dependencies = [
  "anyhow",
  "fastrand",
  "flume",
- "hashlru",
  "icmp-socket2",
  "libc",
  "log",
diff --git a/Cargo.toml b/Cargo.toml
index 80a5247..734430d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -29,7 +29,6 @@ rust-uci = { git = "https://github.com/namib-project/rust-uci.git", rev = "71ea7
 thiserror = "2.0"
 libc = "0.2"
 flume = { version = "0.12.0",  default-features = false, features = ["eventual-fairness", "select"] }
-hashlru = { version = "0.11.1", default-features = false }
 
 [dependencies.log]
 features = ["std"]
diff --git a/src/main.rs b/src/main.rs
index e9f0d23..b893653 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -195,7 +195,8 @@ fn main() -> anyhow::Result<()> {
         "In-flight probe cache capacity: {} (active_reflectors={}, reselection_enabled={}, tick_interval_s={})",
         inflight_probe_capacity, active_reflector_count, reselection_enabled, config.tick_interval
     );
-    let inflight: InFlightProbeCache = InFlightProbeCache::new(inflight_probe_capacity);
+    let inflight: InFlightProbeCache =
+        Arc::new(Mutex::new(HashMap::with_capacity(inflight_probe_capacity)));
 
     let baseliner = Baseliner {
         config: config.clone(),
diff --git a/src/pinger.rs b/src/pinger.rs
index ccfc591..c030039 100644
--- a/src/pinger.rs
+++ b/src/pinger.rs
@@ -1,15 +1,15 @@
 use crate::MeasurementType;
 use crate::SHUTDOWN;
 use crate::metrics::{Metric, MetricsSender};
-use crate::util::RwLockExt;
+use crate::util::{MutexExt, RwLockExt};
 use flume::Sender;
-use hashlru::SyncCache;
 use icmp_socket2::socket::IcmpSocket;
 use icmp_socket2::{IcmpSocket4, Icmpv4Packet};
 use log::{debug, info, warn};
+use std::collections::HashMap;
 use std::net::{IpAddr, Ipv4Addr};
 use std::sync::atomic::Ordering;
-use std::sync::{Arc, RwLock};
+use std::sync::{Arc, Mutex, RwLock};
 use std::time::{Duration, Instant};
 use std::{io, thread};
 use thiserror::Error;
@@ -47,7 +47,8 @@ pub struct InFlightProbe {
 }
 
 pub type InFlightProbeKey = (IpAddr, MeasurementType, u16);
-pub type InFlightProbeCache = SyncCache<InFlightProbeKey, InFlightProbe>;
+pub type InFlightProbeCache = Arc<Mutex<HashMap<InFlightProbeKey, InFlightProbe>>>;
+const INFLIGHT_PROBE_TTL: Duration = Duration::from_secs(30);
 
 fn open_socket(type_: MeasurementType) -> io::Result<IcmpSocket4> {
     match type_ {
@@ -97,15 +98,12 @@ pub trait PingListener {
             };
 
             let key = (addr, type_, reply.seq);
-            let Some(probe) = inflight.remove(&key) else {
+            let Some(probe) = inflight.lock_anyhow()?.remove(&key) else {
                 continue;
             };
             if reply.originate_timestamp != probe.originate_timestamp {
                 continue;
             }
-            if probe.sent_at.elapsed() > Duration::from_secs(30) {
-                continue;
-            }
 
             ping_metrics.send(Metric::Ping {
                 reflector: reply.reflector,
@@ -174,6 +172,10 @@ pub trait PingSender {
                 continue;
             }
 
+            inflight
+                .lock_anyhow()?
+                .retain(|_, probe| probe.sent_at.elapsed() < INFLIGHT_PROBE_TTL);
+
             let sleep_duration =
                 Duration::from_millis((tick_duration_ms / reflectors.len() as u16) as u64);
 
@@ -185,25 +187,22 @@ pub trait PingSender {
 
                 let (packet, originate_timestamp) = self.craft_packet(id, seq);
                 let sent_at = Instant::now();
-                inflight.insert(
-                    (*reflector, type_, seq),
+                let key = (*reflector, type_, seq);
+                inflight.lock_anyhow()?.insert(
+                    key,
                     InFlightProbe {
                         sent_at,
                         originate_timestamp,
                     },
                 );
                 if let Err(e) = socket.send_to(addr, packet) {
-                    inflight.remove(&(*reflector, type_, seq));
+                    inflight.lock_anyhow()?.remove(&key);
                     return Err(e.into());
                 }
                 thread::sleep(sleep_duration);
             }
 
-            if seq == u16::MAX {
-                seq = 0;
-            } else {
-                seq += 1;
-            }
+            seq = seq.wrapping_add(1);
         }
     }