diff --git a/Microsoft.ML.sln b/Microsoft.ML.sln
index 3529c0e5b7..436aedcb0b 100644
--- a/Microsoft.ML.sln
+++ b/Microsoft.ML.sln
@@ -106,6 +106,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.ML.Maml", "src\Mi
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.ML.Console", "src\Microsoft.ML.Console\Microsoft.ML.Console.csproj", "{362A98CF-FBF7-4EBB-A11B-990BBF845B15}"
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.ML.Sweeper.Tests", "test\Microsoft.ML.Sweeper.Tests\Microsoft.ML.Sweeper.Tests.csproj", "{3DEB504D-7A07-48CE-91A2-8047461CB3D4}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -208,6 +210,10 @@ Global
 		{362A98CF-FBF7-4EBB-A11B-990BBF845B15}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{362A98CF-FBF7-4EBB-A11B-990BBF845B15}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{362A98CF-FBF7-4EBB-A11B-990BBF845B15}.Release|Any CPU.Build.0 = Release|Any CPU
+		{3DEB504D-7A07-48CE-91A2-8047461CB3D4}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{3DEB504D-7A07-48CE-91A2-8047461CB3D4}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{3DEB504D-7A07-48CE-91A2-8047461CB3D4}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{3DEB504D-7A07-48CE-91A2-8047461CB3D4}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -243,6 +249,7 @@ Global
 		{7A9DB75F-2CA5-4184-9EF5-1F17EB39483F} = {AED9C836-31E3-4F3F-8ABC-929555D3F3C4}
 		{64F40A0D-D4C2-4AA7-8470-E9CC437827E4} = {09EADF06-BE25-4228-AB53-95AE3E15B530}
 		{362A98CF-FBF7-4EBB-A11B-990BBF845B15} = {09EADF06-BE25-4228-AB53-95AE3E15B530}
+		{3DEB504D-7A07-48CE-91A2-8047461CB3D4} = {AED9C836-31E3-4F3F-8ABC-929555D3F3C4}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {41165AF1-35BB-4832-A189-73060F82B01D}
diff --git a/src/Microsoft.ML.Sweeper/Algorithms/Grid.cs b/src/Microsoft.ML.Sweeper/Algorithms/Grid.cs
index 734cf93e30..b0d4f385db 100644
--- a/src/Microsoft.ML.Sweeper/Algorithms/Grid.cs
+++ b/src/Microsoft.ML.Sweeper/Algorithms/Grid.cs
@@ -64,7 +64,7 @@ protected SweeperBase(ArgumentsBase args, IHostEnvironment env, IValueGenerator[
             SweepParameters = sweepParameters;
         }
 
-        public virtual ParameterSet[] ProposeSweeps(int maxSweeps, IEnumerable<IRunResult> previousRuns)
+        public virtual ParameterSet[] ProposeSweeps(int maxSweeps, IEnumerable<IRunResult> previousRuns = null)
         {
             var prevParamSets = previousRuns?.Select(r => r.ParameterSet).ToList() ?? new List<ParameterSet>();
             var result = new List<ParameterSet>();
@@ -80,12 +80,11 @@ public virtual ParameterSet[] ProposeSweeps(int maxSweeps, IEnumerable<IRunResul
                     (AlreadyGenerated(paramSet, prevParamSets) || AlreadyGenerated(paramSet, result)));
 
                 Contracts.Assert(paramSet != null);
-                result.Add(paramSet);
+                if (!result.Contains(paramSet))
+                    result.Add(paramSet);
             }
-
             return result.ToArray();
         }
-
         protected abstract ParameterSet CreateParamSet();
 
         protected static bool AlreadyGenerated(ParameterSet paramSet, IEnumerable<ParameterSet> previousRuns)
@@ -150,7 +149,7 @@ public RandomGridSweeper(IHostEnvironment env, Arguments args, IValueGenerator[]
             }
         }
 
-        public override ParameterSet[] ProposeSweeps(int maxSweeps, IEnumerable<IRunResult> previousRuns)
+        public override ParameterSet[] ProposeSweeps(int maxSweeps, IEnumerable<IRunResult> previousRuns = null)
         {
             if (_nGridPoints == 0)
                 return base.ProposeSweeps(maxSweeps, previousRuns);
@@ -173,7 +172,8 @@ public override ParameterSet[] ProposeSweeps(int maxSweeps, IEnumerable<IRunResu
                     if (!AlreadyGenerated(_cache[iPerm], prevParamSets))
                         break;
                 }
-                result.Add(_cache[iPerm]);
+                if (!result.Contains(_cache[iPerm]))
+                    result.Add(_cache[iPerm]);
             }
             return result.ToArray();
         }
diff --git a/test/Microsoft.ML.Sweeper.Tests/Microsoft.ML.Sweeper.Tests.csproj b/test/Microsoft.ML.Sweeper.Tests/Microsoft.ML.Sweeper.Tests.csproj
new file mode 100644
index 0000000000..5adf509265
--- /dev/null
+++ b/test/Microsoft.ML.Sweeper.Tests/Microsoft.ML.Sweeper.Tests.csproj
@@ -0,0 +1,22 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netcoreapp2.0</TargetFramework>
+
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.7.0" />
+    <PackageReference Include="xunit" Version="2.3.1" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.3.1" />
+    <DotNetCliToolReference Include="dotnet-xunit" Version="2.3.1" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\Microsoft.ML.PipelineInference\Microsoft.ML.PipelineInference.csproj" />
+    <ProjectReference Include="..\..\src\Microsoft.ML.Sweeper\Microsoft.ML.Sweeper.csproj" />
+    <ProjectReference Include="..\Microsoft.ML.TestFramework\Microsoft.ML.TestFramework.csproj" />
+  </ItemGroup>
+
+</Project>
diff --git a/test/Microsoft.ML.Sweeper.Tests/SweeperUniqueValuesTest.cs b/test/Microsoft.ML.Sweeper.Tests/SweeperUniqueValuesTest.cs
new file mode 100644
index 0000000000..fecd0322ba
--- /dev/null
+++ b/test/Microsoft.ML.Sweeper.Tests/SweeperUniqueValuesTest.cs
@@ -0,0 +1,53 @@
+using Microsoft.ML.Runtime;
+using Microsoft.ML.Runtime.CommandLine;
+using Microsoft.ML.Runtime.Data;
+using Microsoft.ML.Runtime.PipelineInference;
+using Microsoft.ML.Runtime.RunTests;
+using Microsoft.ML.Runtime.Sweeper;
+using System;
+using System.IO;
+using Xunit;
+
+namespace Microsoft.ML.Sweeper.Tests
+{
+    public class SweeperUniqueValuesTest
+    {
+        [Fact]
+        public void SweeperReturnsDistinctValuesForUniformRandomSweeper()
+        {
+            DiscreteValueGenerator valueGenerator = SetSingleParameter();
+            using (var writer = new StreamWriter(new MemoryStream()))
+            using (var env = new TlcEnvironment(42, outWriter: writer, errWriter: writer))
+            {
+                var sweeper = new UniformRandomSweeper(env, new SweeperBase.ArgumentsBase(), new[] { valueGenerator });
+                var results = sweeper.ProposeSweeps(5000);
+                Assert.NotNull(results);
+                int length = results.Length;
+                Assert.Equal(2, length);
+            }
+        }
+        [Fact]
+        public void SweeperReturnsDistinctValuesForRandomGridSweeper()
+        {
+            DiscreteValueGenerator valueGenerator = SetSingleParameter();
+            using (var writer = new StreamWriter(new MemoryStream()))
+            using (var env = new TlcEnvironment(42, outWriter: writer, errWriter: writer))
+            {
+                var sweeper = new RandomGridSweeper(env, new RandomGridSweeper.Arguments(), new[] { valueGenerator });
+                var results = sweeper.ProposeSweeps(5000);
+                Assert.NotNull(results);
+                int length = results.Length;
+                Assert.Equal(2, length);
+            }
+        }
+
+        private static DiscreteValueGenerator SetSingleParameter()
+        {
+            var args = new DiscreteParamArguments();
+            args.Name = "TestParam";
+            args.Values = new string[] { "one", "two" };
+            var valueGenerator = new DiscreteValueGenerator(args);
+            return valueGenerator;
+        }
+    }
+}