diff --git a/src/windows.rs b/src/windows.rs
index 1bf5029..3a47494 100644
--- a/src/windows.rs
+++ b/src/windows.rs
@@ -102,10 +102,10 @@ impl std::convert::TryFrom<ThreadPriority> for WinAPIThreadPriority {
             ThreadPriority::Crossplatform(crate::ThreadPriorityValue(p)) => match p {
                 0 => WinAPIThreadPriority::Idle,
                 1..=19 => WinAPIThreadPriority::Lowest,
-                21..=39 => WinAPIThreadPriority::BelowNormal,
-                41..=59 => WinAPIThreadPriority::Normal,
-                61..=79 => WinAPIThreadPriority::AboveNormal,
-                81..=98 => WinAPIThreadPriority::Highest,
+                20..=39 => WinAPIThreadPriority::BelowNormal,
+                40..=59 => WinAPIThreadPriority::Normal,
+                60..=79 => WinAPIThreadPriority::AboveNormal,
+                80..=98 => WinAPIThreadPriority::Highest,
                 99 => WinAPIThreadPriority::TimeCritical,
                 _ => return Err(Error::Priority("The value is out of range [0; 99].")),
             },
diff --git a/tests/windows.rs b/tests/windows.rs
index 62abb2f..cff6d0d 100644
--- a/tests/windows.rs
+++ b/tests/windows.rs
@@ -6,6 +6,7 @@ use thread_priority::*;
 #[rstest]
 #[case(ThreadPriority::Min, ThreadPriority::Os(WinAPIThreadPriority::Lowest.try_into().unwrap()))]
 #[case(ThreadPriority::Crossplatform(23u8.try_into().unwrap()), ThreadPriority::Os(WinAPIThreadPriority::BelowNormal.try_into().unwrap()))]
+#[case(ThreadPriority::Crossplatform(80u8.try_into().unwrap()), ThreadPriority::Os(WinAPIThreadPriority::Highest.try_into().unwrap()))]
 #[case(ThreadPriority::Max, ThreadPriority::Os(WinAPIThreadPriority::Highest.try_into().unwrap()))]
 fn get_and_set_priority_requires_capabilities(
     #[case] input_priority: ThreadPriority,