diff --git a/Cargo.toml b/Cargo.toml
index 5de8931a1..7922bb99d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -21,6 +21,7 @@ log = "0.4"
 once_cell = "1.5"
 opentelemetry-jaeger = "0.11"
 opentelemetry = "0.12"
+parking_lot = "0.11"
 prost = "0.7"
 prost-types = "0.7"
 slotmap = "1.0"
diff --git a/src/lib.rs b/src/lib.rs
index 284c23417..d872da5fb 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -324,8 +324,6 @@ pub enum CoreError {
     TokioInitError(std::io::Error),
     /// Invalid URI: {0:?}
     InvalidUri(#[from] InvalidUri),
-    /// A mutex was poisoned: {0:?}
-    LockPoisoned(String),
     /// State machines are missing for the workflow with run id {0}!
     MissingMachines(String),
 }
diff --git a/src/workflow/concurrency_manager.rs b/src/workflow/concurrency_manager.rs
index 041afaacb..a356fac83 100644
--- a/src/workflow/concurrency_manager.rs
+++ b/src/workflow/concurrency_manager.rs
@@ -8,9 +8,9 @@ use crate::{
 };
 use crossbeam::channel::{bounded, unbounded, Receiver, Select, Sender, TryRecvError};
 use dashmap::DashMap;
+use parking_lot::Mutex;
 use std::{
     fmt::Debug,
-    sync::Mutex,
     thread::{self, JoinHandle},
 };
 use tracing::Level;
@@ -124,7 +124,6 @@ impl WorkflowConcurrencyManager {
         let _ = self.shutdown_chan.send(true);
         self.wf_thread
             .lock()
-            .expect("Workflow manager thread mutex must be lockable")
             .take()
             .unwrap()
             .join()