diff --git a/Sources/SwiftDiagnostics/Message.swift b/Sources/SwiftDiagnostics/Message.swift
index ea2451fdc3f..5258b794e5b 100644
--- a/Sources/SwiftDiagnostics/Message.swift
+++ b/Sources/SwiftDiagnostics/Message.swift
@@ -26,7 +26,7 @@ public struct MessageID: Hashable, Sendable {
   }
 }
 
-public enum DiagnosticSeverity: Sendable {
+public enum DiagnosticSeverity: Sendable, Hashable {
   case error
   case warning
   case note