diff --git a/UnitySDK/Assets/ML-Agents/Plugins/ProtoBuffer/Grpc.Core.dll.meta b/UnitySDK/Assets/ML-Agents/Plugins/ProtoBuffer/Grpc.Core.dll.meta
index 2a461c7267..3163a0cdcb 100644
--- a/UnitySDK/Assets/ML-Agents/Plugins/ProtoBuffer/Grpc.Core.dll.meta
+++ b/UnitySDK/Assets/ML-Agents/Plugins/ProtoBuffer/Grpc.Core.dll.meta
@@ -8,23 +8,99 @@ PluginImporter:
   isPreloaded: 0
   isOverridable: 0
   platformData:
+  - first:
+      '': Any
+    second:
+      enabled: 0
+      settings:
+        Exclude Android: 1
+        Exclude Editor: 0
+        Exclude Linux: 0
+        Exclude Linux64: 0
+        Exclude LinuxUniversal: 0
+        Exclude OSXUniversal: 0
+        Exclude Win: 0
+        Exclude Win64: 0
+        Exclude iOS: 1
+  - first:
+      Android: Android
+    second:
+      enabled: 0
+      settings:
+        CPU: ARMv7
   - first:
       Any: 
     second:
-      enabled: 1
+      enabled: 0
       settings: {}
   - first:
       Editor: Editor
     second:
-      enabled: 0
+      enabled: 1
       settings:
+        CPU: AnyCPU
         DefaultValueInitialized: true
+        OS: AnyOS
+  - first:
+      Facebook: Win
+    second:
+      enabled: 0
+      settings:
+        CPU: AnyCPU
+  - first:
+      Facebook: Win64
+    second:
+      enabled: 0
+      settings:
+        CPU: AnyCPU
+  - first:
+      Standalone: Linux
+    second:
+      enabled: 1
+      settings:
+        CPU: x86
+  - first:
+      Standalone: Linux64
+    second:
+      enabled: 1
+      settings:
+        CPU: x86_64
+  - first:
+      Standalone: LinuxUniversal
+    second:
+      enabled: 1
+      settings: {}
+  - first:
+      Standalone: OSXUniversal
+    second:
+      enabled: 1
+      settings:
+        CPU: AnyCPU
+  - first:
+      Standalone: Win
+    second:
+      enabled: 1
+      settings:
+        CPU: AnyCPU
+  - first:
+      Standalone: Win64
+    second:
+      enabled: 1
+      settings:
+        CPU: AnyCPU
   - first:
       Windows Store Apps: WindowsStoreApps
     second:
       enabled: 0
       settings:
         CPU: AnyCPU
+  - first:
+      iPhone: iOS
+    second:
+      enabled: 0
+      settings:
+        CompileFlags: 
+        FrameworkDependencies: 
   userData: 
   assetBundleName: 
   assetBundleVariant: 
diff --git a/UnitySDK/Assets/ML-Agents/Scripts/CommunicatorObjects/UnityToExternalGrpc.cs b/UnitySDK/Assets/ML-Agents/Scripts/CommunicatorObjects/UnityToExternalGrpc.cs
index e266ac4935..bf738cbd7a 100644
--- a/UnitySDK/Assets/ML-Agents/Scripts/CommunicatorObjects/UnityToExternalGrpc.cs
+++ b/UnitySDK/Assets/ML-Agents/Scripts/CommunicatorObjects/UnityToExternalGrpc.cs
@@ -2,6 +2,9 @@
 //     Generated by the protocol buffer compiler.  DO NOT EDIT!
 //     source: mlagents/envs/communicator_objects/unity_to_external.proto
 // </auto-generated>
+
+# if UNITY_EDITOR || UNITY_STANDALONE_WIN || UNITY_STANDALONE_OSX || UNITY_STANDALONE_LINUX
+
 #pragma warning disable 1591
 #region Designer generated code
 
@@ -128,3 +131,6 @@ protected override UnityToExternalClient NewInstance(ClientBaseConfiguration con
   }
 }
 #endregion
+
+#endif 
+
diff --git a/UnitySDK/Assets/ML-Agents/Scripts/RpcCommunicator.cs b/UnitySDK/Assets/ML-Agents/Scripts/RpcCommunicator.cs
index 4a1b2fde10..f35cb8c60e 100644
--- a/UnitySDK/Assets/ML-Agents/Scripts/RpcCommunicator.cs
+++ b/UnitySDK/Assets/ML-Agents/Scripts/RpcCommunicator.cs
@@ -1,4 +1,6 @@
+# if UNITY_EDITOR || UNITY_STANDALONE_WIN || UNITY_STANDALONE_OSX || UNITY_STANDALONE_LINUX
 using Grpc.Core;
+#endif
 using System.IO;
 using System.Threading;
 using System.Threading.Tasks;
@@ -16,9 +18,10 @@ public class RPCCommunicator : Communicator
         /// If true, the communication is active.
         bool m_isOpen;
 
+# if UNITY_EDITOR || UNITY_STANDALONE_WIN || UNITY_STANDALONE_OSX || UNITY_STANDALONE_LINUX
         /// The Unity to External client. 
         UnityToExternal.UnityToExternalClient m_client;
-
+#endif
         /// The communicator parameters sent at construction
         CommunicatorParameters m_communicatorParameters;
 
@@ -41,6 +44,7 @@ public RPCCommunicator(CommunicatorParameters communicatorParameters)
         public UnityInput Initialize(UnityOutput unityOutput,
                                      out UnityInput unityInput)
         {
+# if UNITY_EDITOR || UNITY_STANDALONE_WIN || UNITY_STANDALONE_OSX || UNITY_STANDALONE_LINUX
             m_isOpen = true;
             var channel = new Channel(
                 "localhost:"+m_communicatorParameters.port, 
@@ -57,6 +61,10 @@ public UnityInput Initialize(UnityOutput unityOutput,
 #endif
 #endif
             return result.UnityInput;
+#else
+            throw new UnityAgentsException(
+                "You cannot perform training on this platform.");
+#endif
         }
 
         /// <summary>
@@ -64,6 +72,7 @@ public UnityInput Initialize(UnityOutput unityOutput,
         /// </summary>
         public void Close()
         {
+# if UNITY_EDITOR || UNITY_STANDALONE_WIN || UNITY_STANDALONE_OSX || UNITY_STANDALONE_LINUX
             if (!m_isOpen)
             {
                 return;
@@ -78,6 +87,10 @@ public void Close()
             {
                 return;
             }
+#else
+            throw new UnityAgentsException(
+                "You cannot perform training on this platform.");
+#endif
         }
 
         /// <summary>
@@ -87,6 +100,7 @@ public void Close()
         /// <param name="unityOutput">The UnityOutput to be sent.</param>
         public UnityInput Exchange(UnityOutput unityOutput)
         {
+# if UNITY_EDITOR || UNITY_STANDALONE_WIN || UNITY_STANDALONE_OSX || UNITY_STANDALONE_LINUX
             if (!m_isOpen)
             {
                 return null;
@@ -109,6 +123,10 @@ public UnityInput Exchange(UnityOutput unityOutput)
                 m_isOpen = false;
                 return null;
             }
+#else
+            throw new UnityAgentsException(
+                "You cannot perform training on this platform.");
+#endif
         }
 
         /// <summary>
diff --git a/UnitySDK/Assets/ML-Agents/Scripts/SocketCommunicator.cs b/UnitySDK/Assets/ML-Agents/Scripts/SocketCommunicator.cs
index bd13e1751a..a2e6ca6f0e 100644
--- a/UnitySDK/Assets/ML-Agents/Scripts/SocketCommunicator.cs
+++ b/UnitySDK/Assets/ML-Agents/Scripts/SocketCommunicator.cs
@@ -1,5 +1,4 @@
 using Google.Protobuf;
-using Grpc.Core;
 using System.Net.Sockets;
 using UnityEngine;
 using MLAgents.CommunicatorObjects;
diff --git a/protobuf-definitions/README.md b/protobuf-definitions/README.md
index 5141828f42..bc4ca01e92 100644
--- a/protobuf-definitions/README.md
+++ b/protobuf-definitions/README.md
@@ -26,3 +26,15 @@ On Windows & Linux: [See here](https://github.com/google/protobuf/blob/master/sr
 1. Install pre-requisites.
 2. Un-comment line 4 in `make.bat`, and set to correct Grpc.Tools sub-directory.
 3. Run `make.bat`
+4. In the generated `UnityToExternalGrpc.cs` file in the `UnitySDK/Assets/ML-Agents/Scripts/CommunicatorObjects` folder, you will need to add the following to the beginning of the file
+
+```csharp
+# if UNITY_EDITOR || UNITY_STANDALONE_WIN || UNITY_STANDALONE_OSX || UNITY_STANDALONE_LINUX
+```
+ and the following line to the end
+ 
+ ```csharp
+ #endif
+ ```
+This is to make sure the generated code does not try to access the Grpc library
+on platforms that are not supported by Grpc.