diff --git a/Sources/mas/Commands/Upgrade.swift b/Sources/mas/Commands/Upgrade.swift
index 4823976..21ec1ba 100644
--- a/Sources/mas/Commands/Upgrade.swift
+++ b/Sources/mas/Commands/Upgrade.swift
@@ -35,7 +35,6 @@ extension MAS {
             }
 
             guard !apps.isEmpty else {
-                printWarning("Nothing found to upgrade")
                 return
             }
 
@@ -59,14 +58,22 @@ extension MAS {
             let apps =
                 appIDOrNames.isEmpty
                 ? appLibrary.installedApps
-                : appIDOrNames.flatMap { appID in
-                    if let appID = AppID(appID) {
+                : appIDOrNames.flatMap { appIDOrName in
+                    if let appID = AppID(appIDOrName) {
                         // argument is an AppID, lookup apps by id using argument
-                        return appLibrary.installedApps(withAppID: appID)
+                        let installedApps = appLibrary.installedApps(withAppID: appID)
+                        if installedApps.isEmpty {
+                            printError("Unknown app ID \(appID)")
+                        }
+                        return installedApps
                     }
 
                     // argument is not an AppID, lookup apps by name using argument
-                    return appLibrary.installedApps(named: appID)
+                    let installedApps = appLibrary.installedApps(named: appIDOrName)
+                    if installedApps.isEmpty {
+                        printError("Unknown app name '\(appIDOrName)'")
+                    }
+                    return installedApps
                 }
 
             let promises = apps.map { installedApp in
diff --git a/Tests/masTests/Commands/UpgradeSpec.swift b/Tests/masTests/Commands/UpgradeSpec.swift
index 6630777..c3a805f 100644
--- a/Tests/masTests/Commands/UpgradeSpec.swift
+++ b/Tests/masTests/Commands/UpgradeSpec.swift
@@ -25,7 +25,7 @@ public class UpgradeSpec: QuickSpec {
                             .run(appLibrary: MockAppLibrary(), searcher: MockAppStoreSearcher())
                     }
                 }
-                    == "Warning: Nothing found to upgrade\n"
+                .toNot(throwError())
             }
         }
     }