diff --git a/src/lib.rs b/src/lib.rs
index 89afd17..abea3b3 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,19 +5,16 @@ pub use types::{NiceLevel, Priority};
 
 #[derive(thiserror::Error, Debug)]
 pub enum Error {
-    #[error("Permission denied")]
-    PermissionDenied,
+    #[error("Permission denied: {0}")]
+    PermissionDenied(String),
 
-    #[error("Invalid PID")]
-    InvalidPid,
+    #[error("Invalid PID or Thread ID")]
+    InvalidPidOrTid,
 
-    #[error("Invalid thread ID")]
-    InvalidThreadId,
-
-    #[error("Got invalid max priority from RTKit")]
+    #[error("Got invalid max priority from RTKit: {0}")]
     InvalidMaxPriority(i32),
 
-    #[error("Got invalid min nice level from RTKit")]
+    #[error("Got invalid min nice level from RTKit: {0}")]
     InvalidMinNiceLevel(i32),
 
     #[error(transparent)]
@@ -54,8 +51,10 @@ pub fn set_thread_priority(tid: u64, priority: Option<Priority>) -> Result<Prior
         .make_thread_realtime(tid, priority.value())
         .map(|_| priority)
         .map_err(|e| match e {
-            zbus::fdo::Error::AccessDenied(_) => Error::PermissionDenied,
-            e => Error::ZbusMethodError(e),
+            zbus::fdo::Error::AccessDenied(err) => Error::PermissionDenied(err),
+            // NOTE: RTKit returns "No such file or directory" for invalid tids.
+            zbus::fdo::Error::Failed(err) if err == "No such file or directory" => Error::InvalidPidOrTid,
+            err => Error::ZbusMethodError(err),
         })
 }
 
@@ -84,8 +83,10 @@ pub fn set_process_thread_priority(
         .make_thread_realtime_with_pid(pid, tid, priority.value())
         .map(|_| priority)
         .map_err(|e| match e {
-            zbus::fdo::Error::AccessDenied(_) => Error::PermissionDenied,
-            e => Error::ZbusMethodError(e),
+            zbus::fdo::Error::AccessDenied(err) => Error::PermissionDenied(err),
+            // NOTE: RTKit returns "No such file or directory" for invalid tids.
+            zbus::fdo::Error::Failed(err) if err == "No such file or directory" => Error::InvalidPidOrTid,
+            err => Error::ZbusMethodError(err),
         })
 }
 
@@ -118,8 +119,10 @@ pub fn set_thread_nice_level(tid: u64, nice_level: Option<NiceLevel>) -> Result<
         .make_thread_high_priority(tid, nice_level.value())
         .map(|_| nice_level)
         .map_err(|e| match e {
-            zbus::fdo::Error::AccessDenied(_) => Error::PermissionDenied,
-            e => Error::ZbusMethodError(e),
+            zbus::fdo::Error::AccessDenied(err) => Error::PermissionDenied(err),
+            // NOTE: RTKit returns "No such file or directory" for invalid tids.
+            zbus::fdo::Error::Failed(err) if err == "No such file or directory" => Error::InvalidPidOrTid,
+            err => Error::ZbusMethodError(err),
         })
 }
 
@@ -148,7 +151,9 @@ pub fn set_process_thread_nice_level(
         .make_thread_high_priority_with_pid(pid, tid, nice_level.value())
         .map(|_| nice_level)
         .map_err(|e| match e {
-            zbus::fdo::Error::AccessDenied(_) => Error::PermissionDenied,
-            e => Error::ZbusMethodError(e),
+            zbus::fdo::Error::AccessDenied(err) => Error::PermissionDenied(err),
+            // NOTE: RTKit returns "No such file or directory" for invalid tids.
+            zbus::fdo::Error::Failed(err) if err == "No such file or directory" => Error::InvalidPidOrTid,
+            err => Error::ZbusMethodError(err),
         })
 }