diff --git a/.external b/.external
index 1f6f042b77f..e537a336626 100644
--- a/.external
+++ b/.external
@@ -1,2 +1,2 @@
 xamarin/monodroid:d16-4@6f1e0752acdd8ffd250793b84a9c8bc99fa642c8
-mono/mono:2019-06@2c3aeaf3780de7392a0d3cbe4dcf86846eb4dffa
+mono/mono:2019-08@29b1ac19c961b959a09097dbc0fe4cd567cc5298
diff --git a/Configuration.props b/Configuration.props
index 092658754b4..3ef6746d382 100644
--- a/Configuration.props
+++ b/Configuration.props
@@ -79,10 +79,10 @@
     <AndroidSupportedTargetJitAbis Condition=" '$(AndroidSupportedTargetJitAbis)' == '' ">armeabi-v7a:arm64-v8a:x86</AndroidSupportedTargetJitAbis>
     <JavaInteropSourceDirectory Condition=" '$(JavaInteropSourceDirectory)' == '' ">$(MSBuildThisFileDirectory)external\Java.Interop</JavaInteropSourceDirectory>
     <MonoSourceDirectory>$(MSBuildThisFileDirectory)external\mono</MonoSourceDirectory>
-    <MonoRequiredMinimumVersion Condition=" '$(MonoRequiredMinimumVersion)' == '' ">6.4.0</MonoRequiredMinimumVersion>
-    <MonoRequiredMaximumVersion Condition=" '$(MonoRequiredMaximumVersion)' == '' ">6.5.0</MonoRequiredMaximumVersion>
+    <MonoRequiredMinimumVersion Condition=" '$(MonoRequiredMinimumVersion)' == '' ">6.6.0</MonoRequiredMinimumVersion>
+    <MonoRequiredMaximumVersion Condition=" '$(MonoRequiredMaximumVersion)' == '' ">6.7.0</MonoRequiredMaximumVersion>
     <IgnoreMaxMonoVersion Condition=" '$(IgnoreMaxMonoVersion)' == '' ">True</IgnoreMaxMonoVersion>
-    <MonoRequiredDarwinMinimumVersion>$(MonoRequiredMinimumVersion).98</MonoRequiredDarwinMinimumVersion>
+    <MonoRequiredDarwinMinimumVersion>$(MonoRequiredMinimumVersion).54</MonoRequiredDarwinMinimumVersion>
     <LinkerSourceDirectory>$(MSBuildThisFileDirectory)external\mono\sdks\out\android-sources\external\linker\src</LinkerSourceDirectory>
     <OpenTKSourceDirectory>$(MSBuildThisFileDirectory)external\opentk</OpenTKSourceDirectory>
     <MingwZlibRootDirectory Condition=" '$(ZlibRootDirectory)' == '' And '$(HostOS)' == 'Linux' ">\usr</MingwZlibRootDirectory>
diff --git a/build-tools/automation/build.groovy b/build-tools/automation/build.groovy
index be2de2f433e..2e5e083007a 100644
--- a/build-tools/automation/build.groovy
+++ b/build-tools/automation/build.groovy
@@ -146,6 +146,12 @@ timestamps {
                 sh "rm -rf ${packagePath}"
             }
 
+            sh "git clean -xdff"
+            sh "git submodule foreach --recursive git clean -xdff"
+            sh "git submodule foreach --recursive git reset --hard HEAD"
+            sh "git submodule sync"
+            sh "git submodule update --recursive --init --force"
+
             sh "mkdir -p ${packagePath}"
         }
 
diff --git a/external/Java.Interop b/external/Java.Interop
index 75b1189188f..4fd35393fd2 160000
--- a/external/Java.Interop
+++ b/external/Java.Interop
@@ -1 +1 @@
-Subproject commit 75b1189188fe6955493c4eff7cc05ab07485f015
+Subproject commit 4fd35393fd261603e54a87928cfda26e02225d45