diff --git a/osu.Game.Rulesets.Catch/osu.Game.Rulesets.Catch.csproj b/osu.Game.Rulesets.Catch/osu.Game.Rulesets.Catch.csproj
index 5f08048bf9..cdce598ce8 100644
--- a/osu.Game.Rulesets.Catch/osu.Game.Rulesets.Catch.csproj
+++ b/osu.Game.Rulesets.Catch/osu.Game.Rulesets.Catch.csproj
@@ -32,6 +32,10 @@
     <TreatWarningsAsErrors>false</TreatWarningsAsErrors>
   </PropertyGroup>
   <ItemGroup>
+    <Reference Include="JetBrains.Annotations, Version=11.1.0.0, Culture=neutral, PublicKeyToken=1010a0d8d6380325, processorArchitecture=MSIL">
+      <HintPath>$(SolutionDir)\packages\JetBrains.Annotations.11.1.0\lib\net20\JetBrains.Annotations.dll</HintPath>
+      <Private>True</Private>
+    </Reference>
     <Reference Include="nunit.framework, Version=3.8.1.0, Culture=neutral, PublicKeyToken=2638cd05610744eb, processorArchitecture=MSIL">
       <HintPath>$(SolutionDir)\packages\NUnit.3.8.1\lib\net45\nunit.framework.dll</HintPath>
       <Private>True</Private>
diff --git a/osu.Game.Rulesets.Catch/packages.config b/osu.Game.Rulesets.Catch/packages.config
index b39a85a382..e67d3e9b34 100644
--- a/osu.Game.Rulesets.Catch/packages.config
+++ b/osu.Game.Rulesets.Catch/packages.config
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <packages>
+  <package id="JetBrains.Annotations" version="11.1.0" targetFramework="net461" />
   <package id="NUnit" version="3.8.1" targetFramework="net461" />
   <package id="ppy.OpenTK" version="3.0.11" targetFramework="net461" />
 </packages>
\ No newline at end of file
diff --git a/osu.Game.Rulesets.Mania/osu.Game.Rulesets.Mania.csproj b/osu.Game.Rulesets.Mania/osu.Game.Rulesets.Mania.csproj
index 9b6b546b5f..b9e7f8e60f 100644
--- a/osu.Game.Rulesets.Mania/osu.Game.Rulesets.Mania.csproj
+++ b/osu.Game.Rulesets.Mania/osu.Game.Rulesets.Mania.csproj
@@ -32,6 +32,10 @@
     <TreatWarningsAsErrors>false</TreatWarningsAsErrors>
   </PropertyGroup>
   <ItemGroup>
+    <Reference Include="JetBrains.Annotations, Version=11.1.0.0, Culture=neutral, PublicKeyToken=1010a0d8d6380325, processorArchitecture=MSIL">
+      <HintPath>$(SolutionDir)\packages\JetBrains.Annotations.11.1.0\lib\net20\JetBrains.Annotations.dll</HintPath>
+      <Private>True</Private>
+    </Reference>
     <Reference Include="nunit.framework, Version=3.8.1.0, Culture=neutral, PublicKeyToken=2638cd05610744eb, processorArchitecture=MSIL">
       <HintPath>$(SolutionDir)\packages\NUnit.3.8.1\lib\net45\nunit.framework.dll</HintPath>
       <Private>True</Private>
diff --git a/osu.Game.Rulesets.Mania/packages.config b/osu.Game.Rulesets.Mania/packages.config
index b39a85a382..e67d3e9b34 100644
--- a/osu.Game.Rulesets.Mania/packages.config
+++ b/osu.Game.Rulesets.Mania/packages.config
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <packages>
+  <package id="JetBrains.Annotations" version="11.1.0" targetFramework="net461" />
   <package id="NUnit" version="3.8.1" targetFramework="net461" />
   <package id="ppy.OpenTK" version="3.0.11" targetFramework="net461" />
 </packages>
\ No newline at end of file
diff --git a/osu.Game.Rulesets.Osu/osu.Game.Rulesets.Osu.csproj b/osu.Game.Rulesets.Osu/osu.Game.Rulesets.Osu.csproj
index a59d4607df..74a3883f0a 100644
--- a/osu.Game.Rulesets.Osu/osu.Game.Rulesets.Osu.csproj
+++ b/osu.Game.Rulesets.Osu/osu.Game.Rulesets.Osu.csproj
@@ -33,6 +33,10 @@
     <TreatWarningsAsErrors>false</TreatWarningsAsErrors>
   </PropertyGroup>
   <ItemGroup>
+    <Reference Include="JetBrains.Annotations, Version=11.1.0.0, Culture=neutral, PublicKeyToken=1010a0d8d6380325, processorArchitecture=MSIL">
+      <HintPath>$(SolutionDir)\packages\JetBrains.Annotations.11.1.0\lib\net20\JetBrains.Annotations.dll</HintPath>
+      <Private>True</Private>
+    </Reference>
     <Reference Include="nunit.framework, Version=3.8.1.0, Culture=neutral, PublicKeyToken=2638cd05610744eb, processorArchitecture=MSIL">
       <HintPath>$(SolutionDir)\packages\NUnit.3.8.1\lib\net45\nunit.framework.dll</HintPath>
       <Private>True</Private>
diff --git a/osu.Game.Rulesets.Osu/packages.config b/osu.Game.Rulesets.Osu/packages.config
index b39a85a382..e67d3e9b34 100644
--- a/osu.Game.Rulesets.Osu/packages.config
+++ b/osu.Game.Rulesets.Osu/packages.config
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <packages>
+  <package id="JetBrains.Annotations" version="11.1.0" targetFramework="net461" />
   <package id="NUnit" version="3.8.1" targetFramework="net461" />
   <package id="ppy.OpenTK" version="3.0.11" targetFramework="net461" />
 </packages>
\ No newline at end of file
diff --git a/osu.Game.Rulesets.Taiko/osu.Game.Rulesets.Taiko.csproj b/osu.Game.Rulesets.Taiko/osu.Game.Rulesets.Taiko.csproj
index 36ac9384cf..90256c7d63 100644
--- a/osu.Game.Rulesets.Taiko/osu.Game.Rulesets.Taiko.csproj
+++ b/osu.Game.Rulesets.Taiko/osu.Game.Rulesets.Taiko.csproj
@@ -32,6 +32,10 @@
     <TreatWarningsAsErrors>false</TreatWarningsAsErrors>
   </PropertyGroup>
   <ItemGroup>
+    <Reference Include="JetBrains.Annotations, Version=11.1.0.0, Culture=neutral, PublicKeyToken=1010a0d8d6380325, processorArchitecture=MSIL">
+      <HintPath>$(SolutionDir)\packages\JetBrains.Annotations.11.1.0\lib\net20\JetBrains.Annotations.dll</HintPath>
+      <Private>True</Private>
+    </Reference>
     <Reference Include="nunit.framework, Version=3.8.1.0, Culture=neutral, PublicKeyToken=2638cd05610744eb, processorArchitecture=MSIL">
       <HintPath>$(SolutionDir)\packages\NUnit.3.8.1\lib\net45\nunit.framework.dll</HintPath>
       <Private>True</Private>
diff --git a/osu.Game.Rulesets.Taiko/packages.config b/osu.Game.Rulesets.Taiko/packages.config
index b39a85a382..e67d3e9b34 100644
--- a/osu.Game.Rulesets.Taiko/packages.config
+++ b/osu.Game.Rulesets.Taiko/packages.config
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <packages>
+  <package id="JetBrains.Annotations" version="11.1.0" targetFramework="net461" />
   <package id="NUnit" version="3.8.1" targetFramework="net461" />
   <package id="ppy.OpenTK" version="3.0.11" targetFramework="net461" />
 </packages>
\ No newline at end of file
diff --git a/osu.Game.Tests/osu.Game.Tests.csproj b/osu.Game.Tests/osu.Game.Tests.csproj
index 059adc6d55..d30241fae4 100644
--- a/osu.Game.Tests/osu.Game.Tests.csproj
+++ b/osu.Game.Tests/osu.Game.Tests.csproj
@@ -33,6 +33,10 @@
     <Reference Include="DeepEqual, Version=1.6.0.0, Culture=neutral, PublicKeyToken=null">
       <HintPath>$(SolutionDir)\packages\DeepEqual.1.6.0.0\lib\net40\DeepEqual.dll</HintPath>
     </Reference>
+    <Reference Include="JetBrains.Annotations, Version=11.1.0.0, Culture=neutral, PublicKeyToken=1010a0d8d6380325, processorArchitecture=MSIL">
+      <HintPath>$(SolutionDir)\packages\JetBrains.Annotations.11.1.0\lib\net20\JetBrains.Annotations.dll</HintPath>
+      <Private>True</Private>
+    </Reference>
     <Reference Include="nunit.framework, Version=3.8.1.0, Culture=neutral, PublicKeyToken=2638cd05610744eb, processorArchitecture=MSIL">
       <HintPath>$(SolutionDir)\packages\NUnit.3.8.1\lib\net45\nunit.framework.dll</HintPath>
       <Private>True</Private>
diff --git a/osu.Game.Tests/packages.config b/osu.Game.Tests/packages.config
index 62ddb99609..71c79cd26e 100644
--- a/osu.Game.Tests/packages.config
+++ b/osu.Game.Tests/packages.config
@@ -5,6 +5,7 @@ Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/maste
 -->
 <packages>
   <package id="DeepEqual" version="1.6.0.0" targetFramework="net461" />
+  <package id="JetBrains.Annotations" version="11.1.0" targetFramework="net461" />
   <package id="NUnit" version="3.8.1" targetFramework="net461" />
   <package id="ppy.OpenTK" version="3.0.11" targetFramework="net461" />
   <package id="System.ValueTuple" version="4.4.0" targetFramework="net461" />
diff --git a/osu.Game/osu.Game.csproj b/osu.Game/osu.Game.csproj
index 7f88f65a24..12ca9e5de7 100644
--- a/osu.Game/osu.Game.csproj
+++ b/osu.Game/osu.Game.csproj
@@ -91,6 +91,10 @@
     <Reference Include="Humanizer, Version=2.2.0.0, Culture=neutral, PublicKeyToken=979442b78dfc278e, processorArchitecture=MSIL">
       <HintPath>$(SolutionDir)\packages\Humanizer.Core.2.2.0\lib\netstandard1.0\Humanizer.dll</HintPath>
     </Reference>
+    <Reference Include="JetBrains.Annotations, Version=11.1.0.0, Culture=neutral, PublicKeyToken=1010a0d8d6380325, processorArchitecture=MSIL">
+      <HintPath>$(SolutionDir)\packages\JetBrains.Annotations.11.1.0\lib\net20\JetBrains.Annotations.dll</HintPath>
+      <Private>True</Private>
+    </Reference>
     <Reference Include="Microsoft.Data.Sqlite, Version=2.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60, processorArchitecture=MSIL">
       <HintPath>$(SolutionDir)\packages\Microsoft.Data.Sqlite.Core.2.0.0\lib\netstandard2.0\Microsoft.Data.Sqlite.dll</HintPath>
     </Reference>
diff --git a/osu.Game/packages.config b/osu.Game/packages.config
index 2938739eef..0216c8ae67 100644
--- a/osu.Game/packages.config
+++ b/osu.Game/packages.config
@@ -47,6 +47,7 @@ Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/maste
   <package id="Humanizer.Core.zh-CN" version="2.2.0" targetFramework="net461" />
   <package id="Humanizer.Core.zh-Hans" version="2.2.0" targetFramework="net461" />
   <package id="Humanizer.Core.zh-Hant" version="2.2.0" targetFramework="net461" />
+  <package id="JetBrains.Annotations" version="11.1.0" targetFramework="net461" />
   <package id="Microsoft.CSharp" version="4.4.0" targetFramework="net461" />
   <package id="Microsoft.Data.Sqlite.Core" version="2.0.0" targetFramework="net461" />
   <package id="Microsoft.EntityFrameworkCore" version="2.0.0" targetFramework="net461" />