diff --git a/NuKeeper.Inspection.Tests/NuGetApi/ApiPackageLookupTests.cs b/NuKeeper.Inspection.Tests/NuGetApi/ApiPackageLookupTests.cs
index 7da1ef855..829b3fc16 100644
--- a/NuKeeper.Inspection.Tests/NuGetApi/ApiPackageLookupTests.cs
+++ b/NuKeeper.Inspection.Tests/NuGetApi/ApiPackageLookupTests.cs
@@ -4,6 +4,7 @@
 using NSubstitute;
 using NuGet.Packaging.Core;
 using NuGet.Versioning;
+using NuKeeper.Abstractions;
 using NuKeeper.Abstractions.Configuration;
 using NuKeeper.Abstractions.NuGet;
 using NuKeeper.Abstractions.NuGetApi;
@@ -16,20 +17,18 @@ namespace NuKeeper.Inspection.Tests.NuGetApi
     public class ApiPackageLookupTests
     {
         [Test]
-        public async Task WhenNoPackagesAreFound()
+        public void WhenNoPackagesAreFound()
         {
             var allVersionsLookup = MockVersionLookup(new List<PackageSearchMetadata>());
             IApiPackageLookup lookup = new ApiPackageLookup(allVersionsLookup);
 
-            var updates = await lookup.FindVersionUpdate(
-                CurrentVersion123("TestPackage"),
-                NuGetSources.GlobalFeed,
-                VersionChange.Major,
-                UsePrerelease.FromPrerelease);
-
-            Assert.That(updates, Is.Not.Null);
-            Assert.That(updates.Major, Is.Null);
-            Assert.That(updates.Selected(), Is.Null);
+            var exception = Assert.ThrowsAsync<NuKeeperException>(async () =>
+                await lookup.FindVersionUpdate(
+                    CurrentVersion123("TestPackage"),
+                    NuGetSources.GlobalFeed,
+                    VersionChange.Major,
+                    UsePrerelease.FromPrerelease));
+            Assert.That(exception.Message, Is.EqualTo("Could not find package TestPackage.1.2.3 in these sources: https://api.nuget.org/v3/index.json"));
         }
 
         [Test]
diff --git a/NuKeeper.Inspection/NuGetApi/ApiPackageLookup.cs b/NuKeeper.Inspection/NuGetApi/ApiPackageLookup.cs
index ba4768da1..efe69ac81 100644
--- a/NuKeeper.Inspection/NuGetApi/ApiPackageLookup.cs
+++ b/NuKeeper.Inspection/NuGetApi/ApiPackageLookup.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Linq;
 using System.Threading.Tasks;
 using NuGet.Packaging.Core;
 using NuKeeper.Abstractions;
@@ -31,6 +32,10 @@ public async Task<PackageLookupResult> FindVersionUpdate(
             var includePrerelease = ShouldAllowPrerelease(package, usePrerelease);
 
             var foundVersions = await _packageVersionsLookup.Lookup(package.Id, includePrerelease, sources);
+
+            if (!foundVersions.Any())
+                throw new NuKeeperException($"Could not find package {package} in these sources: {sources}");
+
             return VersionChanges.MakeVersions(package.Version, foundVersions, allowedChange);
         }
 
diff --git a/NuKeeper.Integration.Tests/NuGet/Api/ApiPackageLookupTests.cs b/NuKeeper.Integration.Tests/NuGet/Api/ApiPackageLookupTests.cs
index 413ffd0e8..a8421282c 100644
--- a/NuKeeper.Integration.Tests/NuGet/Api/ApiPackageLookupTests.cs
+++ b/NuKeeper.Integration.Tests/NuGet/Api/ApiPackageLookupTests.cs
@@ -1,5 +1,6 @@
 using NuGet.Packaging.Core;
 using NuGet.Versioning;
+using NuKeeper.Abstractions;
 using NuKeeper.Abstractions.Configuration;
 using NuKeeper.Abstractions.NuGet;
 using NuKeeper.Inspection.NuGetApi;
@@ -33,19 +34,17 @@ public async Task AmbiguousPackageName_ShouldReturnCorrectResult()
         }
 
         [Test]
-        public async Task UnknownPackageName_ShouldNotReturnResult()
+        public void UnknownPackageName_ShouldNotReturnResult()
         {
             var lookup = BuildPackageLookup();
 
-            var package = await lookup.FindVersionUpdate(
-                Current(Guid.NewGuid().ToString()),
-                NuGetSources.GlobalFeed,
-                VersionChange.Major,
-                UsePrerelease.FromPrerelease);
-
-            Assert.That(package, Is.Not.Null);
-            Assert.That(package.Major, Is.Null);
-            Assert.That(package.Selected(), Is.Null);
+            var exception = Assert.ThrowsAsync<NuKeeperException>(async () =>
+                await lookup.FindVersionUpdate(
+                    Current(Guid.NewGuid().ToString()),
+                    NuGetSources.GlobalFeed,
+                    VersionChange.Major,
+                    UsePrerelease.FromPrerelease));
+            Assert.That(exception.Message, Does.Match("Could not find package (.+?) in these sources: https://api.nuget.org/v3/index.json"));
         }
 
         [Test]
diff --git a/NuKeeper.Integration.Tests/NuGet/Api/BulkPackageLookupTests.cs b/NuKeeper.Integration.Tests/NuGet/Api/BulkPackageLookupTests.cs
index 60313b968..6c4270a99 100644
--- a/NuKeeper.Integration.Tests/NuGet/Api/BulkPackageLookupTests.cs
+++ b/NuKeeper.Integration.Tests/NuGet/Api/BulkPackageLookupTests.cs
@@ -1,5 +1,6 @@
 using NuGet.Packaging.Core;
 using NuGet.Versioning;
+using NuKeeper.Abstractions;
 using NuKeeper.Abstractions.Configuration;
 using NuKeeper.Abstractions.NuGet;
 using NuKeeper.Inspection.NuGetApi;
@@ -73,7 +74,7 @@ public async Task FindsSingleUpdateForPackageDifferingOnlyByCase()
         }
 
         [Test]
-        public async Task InvalidPackageIsIgnored()
+        public void InvalidPackageThrows()
         {
             var packages = new List<PackageIdentity>
             {
@@ -82,12 +83,11 @@ public async Task InvalidPackageIsIgnored()
 
             var lookup = BuildBulkPackageLookup();
 
-            var results = await lookup.FindVersionUpdates(
-                packages, NuGetSources.GlobalFeed, VersionChange.Major,
-                UsePrerelease.FromPrerelease);
-
-            Assert.That(results, Is.Not.Null);
-            Assert.That(results, Is.Empty);
+            var exception = Assert.ThrowsAsync<NuKeeperException>(async () =>
+                await lookup.FindVersionUpdates(
+                    packages, NuGetSources.GlobalFeed, VersionChange.Major,
+                    UsePrerelease.FromPrerelease));
+            Assert.That(exception.Message, Does.Match("Could not find package (.+?) in these sources: https://api.nuget.org/v3/index.json"));
         }
 
         [Test]
@@ -103,30 +103,6 @@ public async Task TestEmptyList()
             Assert.That(results, Is.Empty);
         }
 
-        [Test]
-        public async Task ValidPackagesWorkDespiteInvalidPackages()
-        {
-            var packages = new List<PackageIdentity>
-            {
-                Current("Moq"),
-                Current(Guid.NewGuid().ToString()),
-                Current("Newtonsoft.Json"),
-                Current(Guid.NewGuid().ToString())
-            };
-
-            var lookup = BuildBulkPackageLookup();
-
-            var results = await lookup.FindVersionUpdates(
-                packages, NuGetSources.GlobalFeed, VersionChange.Major,
-                UsePrerelease.FromPrerelease);
-
-            var updatedPackages = results.Select(p => p.Key);
-            Assert.That(results, Is.Not.Null);
-            Assert.That(results.Count, Is.EqualTo(2));
-            Assert.That(updatedPackages, Has.Some.Matches<PackageIdentity>(p => p.Id == "Moq"));
-            Assert.That(updatedPackages, Has.Some.Matches<PackageIdentity>(p => p.Id == "Newtonsoft.Json"));
-        }
-
         private BulkPackageLookup BuildBulkPackageLookup()
         {
             var lookup = new ApiPackageLookup(new PackageVersionsLookup(NugetLogger, NukeeperLogger));
diff --git a/NuKeeper/ExitCodes.cs b/NuKeeper/ExitCodes.cs
index c257bed2a..34b21f2a5 100644
--- a/NuKeeper/ExitCodes.cs
+++ b/NuKeeper/ExitCodes.cs
@@ -8,5 +8,6 @@ enum ExitCodes
         Success = 0,
         UnknownError = 1 << 0,
         InvalidArguments = 1 << 1,
+        OtherError = 1 << 2,
     }
 }
diff --git a/NuKeeper/Program.cs b/NuKeeper/Program.cs
index 2d7dadd3a..81f58117d 100644
--- a/NuKeeper/Program.cs
+++ b/NuKeeper/Program.cs
@@ -1,4 +1,5 @@
 using McMaster.Extensions.CommandLineUtils;
+using NuKeeper.Abstractions;
 using NuKeeper.Commands;
 using System;
 using System.Reflection;
@@ -39,6 +40,11 @@ public static async Task<int> Main(string[] args)
                 Console.WriteLine(cpe.Message);
                 return (int)ExitCodes.InvalidArguments;
             }
+            catch (NuKeeperException nke)
+            {
+                 Console.WriteLine(nke.Message);
+                 return (int)ExitCodes.OtherError;
+            }
             catch (Exception ex)
             {
                 Console.WriteLine(ex.ToString());