diff --git a/eng/Versions.props b/eng/Versions.props
index 49b62053b6b7e..7b1acb2136333 100644
--- a/eng/Versions.props
+++ b/eng/Versions.props
@@ -47,7 +47,7 @@
     <EnvDTE80Version>8.0.0</EnvDTE80Version>
     <FakeSignVersion>0.9.2</FakeSignVersion>
     <HumanizerCoreVersion>2.2.0</HumanizerCoreVersion>
-    <ICSharpCodeDecompilerVersion>5.0.2.5153</ICSharpCodeDecompilerVersion>
+    <ICSharpCodeDecompilerVersion>6.1.0.5902</ICSharpCodeDecompilerVersion>
     <MicrosoftBuildVersion>15.3.409</MicrosoftBuildVersion>
     <MicrosoftBuildFrameworkVersion>15.3.409</MicrosoftBuildFrameworkVersion>
     <MicrosoftBuildLocatorVersion>1.2.6</MicrosoftBuildLocatorVersion>
diff --git a/src/EditorFeatures/CSharp/DecompiledSource/AssemblyResolver.cs b/src/EditorFeatures/CSharp/DecompiledSource/AssemblyResolver.cs
index d3d6bb7d07caa..53385de0c6113 100644
--- a/src/EditorFeatures/CSharp/DecompiledSource/AssemblyResolver.cs
+++ b/src/EditorFeatures/CSharp/DecompiledSource/AssemblyResolver.cs
@@ -41,6 +41,12 @@ void BuildReferenceCache()
             }
         }
 
+        bool IAssemblyResolver.IsGacAssembly(IAssemblyReference reference)
+        {
+            // This method is not called by the decompiler
+            throw new NotSupportedException();
+        }
+
         public PEFile Resolve(IAssemblyReference name)
         {
             Log("------------------");