diff --git a/src/Compilers/CSharp/Portable/Symbols/ModuleSymbol.cs b/src/Compilers/CSharp/Portable/Symbols/ModuleSymbol.cs
index c44936986ba05f2ab3d2ec727325596f8ef90f19..97fc526af7047b0406fc82f7ac4d639a09894a3e 100644
--- a/src/Compilers/CSharp/Portable/Symbols/ModuleSymbol.cs
+++ b/src/Compilers/CSharp/Portable/Symbols/ModuleSymbol.cs
@@ -359,7 +359,7 @@ ImmutableArray<IAssemblySymbol> IModuleSymbol.ReferencedAssemblySymbols
         {
             get
             {
-                return ImmutableArray<IAssemblySymbol>.CastUp(ReferencedAssemblySymbols);
+                return ImmutableArray.Create<IAssemblySymbol, AssemblySymbol>(ReferencedAssemblySymbols);
             }
         }
 
diff --git a/src/Compilers/Core/Desktop/CommandLine/CommonCompiler.cs b/src/Compilers/Core/Desktop/CommandLine/CommonCompiler.cs
index 989c7b823353b4ecaadcf86e523c8afa61811a33..fb569c2c91aef1ab30a65d8165aac4d80b352514 100644
--- a/src/Compilers/Core/Desktop/CommandLine/CommonCompiler.cs
+++ b/src/Compilers/Core/Desktop/CommandLine/CommonCompiler.cs
@@ -333,7 +333,7 @@ private int RunCore(TextWriter consoleOutput, CancellationToken cancellationToke
 
             cancellationToken.ThrowIfCancellationRequested();
 
-            var analyzerOptions = new AnalyzerOptions(ImmutableArray<AdditionalText>.CastUp(additionalTextFiles));
+            var analyzerOptions = new AnalyzerOptions(ImmutableArray.Create<AdditionalText, AdditionalTextFile>(additionalTextFiles));
 
             AnalyzerDriver analyzerDriver = null;
             AnalyzerManager analyzerManager = null;
diff --git a/src/Compilers/Core/Portable/Collections/ImmutableArrayExtensions.cs b/src/Compilers/Core/Portable/Collections/ImmutableArrayExtensions.cs
index 2bca4cf5127c2c77aae611c1163f087099b46082..c85d49ffd804fd9385d365856fc6de94ae4fd77e 100644
--- a/src/Compilers/Core/Portable/Collections/ImmutableArrayExtensions.cs
+++ b/src/Compilers/Core/Portable/Collections/ImmutableArrayExtensions.cs
@@ -266,7 +266,7 @@ public static ImmutableArray<T> WhereAsArray<T>(this ImmutableArray<T> array, Fu
         public static ImmutableArray<TBase> Cast<TDerived, TBase>(this ImmutableArray<TDerived> items)
             where TDerived : class, TBase
         {
-            return ImmutableArray<TBase>.CastUp(items);
+            return ImmutableArray.Create<TBase, TDerived>(items);
         }
 
         /// <summary>
diff --git a/src/Compilers/Core/Portable/Collections/StaticCast.cs b/src/Compilers/Core/Portable/Collections/StaticCast.cs
index 2cfb6fce8b98105e5113f2f450a0cc0a843e1c68..403149f1ff6a7f4c34b8cf5c0032d956c1cdf0cd 100644
--- a/src/Compilers/Core/Portable/Collections/StaticCast.cs
+++ b/src/Compilers/Core/Portable/Collections/StaticCast.cs
@@ -8,7 +8,7 @@ internal static class StaticCast<T>
     {
         internal static ImmutableArray<T> From<TDerived>(ImmutableArray<TDerived> from) where TDerived : class, T
         {
-            return ImmutableArray<T>.CastUp(from);
+            return ImmutableArray.Create<T, TDerived>(from);
         }
     }
 }
diff --git a/src/Compilers/Core/SharedCollections/ArrayBuilder.cs b/src/Compilers/Core/SharedCollections/ArrayBuilder.cs
index d5e63009f64a8c9a5e4b58d5050ca475e7990d88..f69e1ce70ea2a346752ad0808dbc969d7ddfa302 100644
--- a/src/Compilers/Core/SharedCollections/ArrayBuilder.cs
+++ b/src/Compilers/Core/SharedCollections/ArrayBuilder.cs
@@ -101,10 +101,7 @@ public void Insert(int index, T item)
 
         public void EnsureCapacity(int capacity)
         {
-            if (_builder.Capacity < capacity)
-            {
-                _builder.Capacity = capacity;
-            }
+            _builder.EnsureCapacity(capacity);
         }
 
         public void Clear()
@@ -134,7 +131,7 @@ public void RemoveLast()
 
         public void ReverseContents()
         {
-            _builder.Reverse();
+            _builder.ReverseContents();
         }
 
         public void Sort()
diff --git a/src/Compilers/VisualBasic/Portable/Binding/Binder_Lookup.vb b/src/Compilers/VisualBasic/Portable/Binding/Binder_Lookup.vb
index dbc34db510c7b3bb6bf0d28b60886ccbec241534..bb1c619f8b60c70ce8eefbeff9128e40cd210d5e 100644
--- a/src/Compilers/VisualBasic/Portable/Binding/Binder_Lookup.vb
+++ b/src/Compilers/VisualBasic/Portable/Binding/Binder_Lookup.vb
@@ -2020,7 +2020,7 @@ ExitForFor:
                     ' Only named types have members that are types. Go through all the types in this type and
                     ' validate them. If there's multiple, give an error.
                     If TypeOf container Is NamedTypeSymbol Then
-                        members = ImmutableArray(Of Symbol).CastUp(container.GetTypeMembers(name))
+                        members = ImmutableArray.Create(Of Symbol, NamedTypeSymbol)(container.GetTypeMembers(name))
                     End If
                 ElseIf (options And LookupOptions.LabelsOnly) = 0 Then
                     members = container.GetMembers(name)
diff --git a/src/Compilers/VisualBasic/Portable/Symbols/MethodSymbol.vb b/src/Compilers/VisualBasic/Portable/Symbols/MethodSymbol.vb
index 70a1320b09fb76869f527b6169e36798c9ced9c5..0de227ab856b02aa838d4644e5245c133d350b1f 100644
--- a/src/Compilers/VisualBasic/Portable/Symbols/MethodSymbol.vb
+++ b/src/Compilers/VisualBasic/Portable/Symbols/MethodSymbol.vb
@@ -817,7 +817,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols
 
         Private ReadOnly Property IMethodSymbol_Parameters As ImmutableArray(Of IParameterSymbol) Implements IMethodSymbol.Parameters
             Get
-                Return ImmutableArray(Of IParameterSymbol).CastUp(Me.Parameters)
+                Return ImmutableArray.Create(Of IParameterSymbol, ParameterSymbol)(Me.Parameters)
             End Get
         End Property
 
diff --git a/src/Compilers/VisualBasic/Portable/Symbols/ModuleSymbol.vb b/src/Compilers/VisualBasic/Portable/Symbols/ModuleSymbol.vb
index f7dd5441cbf22834fa4aee02b860b6af23a69917..673603a0e748fd0ad1f7e91149cea6a26e44fe56 100644
--- a/src/Compilers/VisualBasic/Portable/Symbols/ModuleSymbol.vb
+++ b/src/Compilers/VisualBasic/Portable/Symbols/ModuleSymbol.vb
@@ -290,7 +290,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols
 
         Private ReadOnly Property IModuleSymbol_ReferencedAssemblySymbols As ImmutableArray(Of IAssemblySymbol) Implements IModuleSymbol.ReferencedAssemblySymbols
             Get
-                Return ImmutableArray(Of IAssemblySymbol).CastUp(ReferencedAssemblySymbols)
+                Return ImmutableArray.Create(Of IAssemblySymbol, AssemblySymbol)(ReferencedAssemblySymbols)
             End Get
         End Property
 
diff --git a/src/Compilers/VisualBasic/Portable/Symbols/Source/SourceNamespaceSymbol.vb b/src/Compilers/VisualBasic/Portable/Symbols/Source/SourceNamespaceSymbol.vb
index 645569c4b117c3799318fd55c8d742eb54c179c4..c1b6e1e653dfe3435148686ace1f5716764487e5 100644
--- a/src/Compilers/VisualBasic/Portable/Symbols/Source/SourceNamespaceSymbol.vb
+++ b/src/Compilers/VisualBasic/Portable/Symbols/Source/SourceNamespaceSymbol.vb
@@ -332,7 +332,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols
         Public Overloads Overrides Function GetMembers(name As String) As ImmutableArray(Of Symbol)
             Dim members As ImmutableArray(Of NamespaceOrTypeSymbol) = Nothing
             If Me.GetNameToMembersMap().TryGetValue(name, members) Then
-                Return ImmutableArray(Of Symbol).CastUp(members)
+                Return ImmutableArray.Create(Of Symbol, NamespaceOrTypeSymbol)(members)
             Else
                 Return ImmutableArray(Of Symbol).Empty
             End If