Use IReadOnlyCollection.

3 files changed, 3 insertions, 3 deletions

diff --git a/global.json b/global.json
index e30536fb..5543c0a8 100644
--- a/global.json
+++ b/global.json
@@ -1,6 +1,6 @@
 {
   "msbuild-sdks": {
-    "WixToolset.Sdk": "4.0.0-build-0209"
+    "WixToolset.Sdk": "4.0.0-build-0210"
   },
   "sdk": {
     "allowPrerelease": false
diff --git a/src/wixext/BalBurnBackendExtension.cs b/src/wixext/BalBurnBackendExtension.cs
index 6e639c1b..e8dc7a3e 100644
--- a/src/wixext/BalBurnBackendExtension.cs
+++ b/src/wixext/BalBurnBackendExtension.cs
@@ -25,7 +25,7 @@ namespace WixToolset.Bal
             BalSymbolDefinitions.WixStdbaOverridableVariable,
         };
 
-        protected override IEnumerable<IntermediateSymbolDefinition> SymbolDefinitions => BurnSymbolDefinitions;
+        protected override IReadOnlyCollection<IntermediateSymbolDefinition> SymbolDefinitions => BurnSymbolDefinitions;
 
         public override void SymbolsFinalized(IntermediateSection section)
         {
diff --git a/src/wixext/BalExtensionFactory.cs b/src/wixext/BalExtensionFactory.cs
index 30ec88c3..0bfb6c5f 100644
--- a/src/wixext/BalExtensionFactory.cs
+++ b/src/wixext/BalExtensionFactory.cs
@@ -8,7 +8,7 @@ namespace WixToolset.Bal
 
     public class BalExtensionFactory : BaseExtensionFactory
     {
-        protected override IEnumerable<Type> ExtensionTypes => new[]
+        protected override IReadOnlyCollection<Type> ExtensionTypes => new[]
         {
             typeof(BalCompiler),
             typeof(BalExtensionData),