diff --git a/src/Microsoft.Health.Fhir.Shared.Api/Features/Formatters/FormatParametersValidator.cs b/src/Microsoft.Health.Fhir.Shared.Api/Features/Formatters/FormatParametersValidator.cs
index b41f7cd69a..bb4b1cc847 100644
--- a/src/Microsoft.Health.Fhir.Shared.Api/Features/Formatters/FormatParametersValidator.cs
+++ b/src/Microsoft.Health.Fhir.Shared.Api/Features/Formatters/FormatParametersValidator.cs
@@ -33,7 +33,7 @@ namespace Microsoft.Health.Fhir.Api.Features.Formatters
     public sealed class FormatParametersValidator : IFormatParametersValidator
     {
         private readonly IConformanceProvider _conformanceProvider;
-        private readonly ICollection<TextOutputFormatter> _outputFormatters;
+        private readonly IEnumerable<TextOutputFormatter> _outputFormatters;
         private readonly ConcurrentDictionary<ResourceFormat, bool> _supportedFormats = new ConcurrentDictionary<ResourceFormat, bool>();
         private readonly ConcurrentDictionary<string, bool> _supportedPatchFormats = new ConcurrentDictionary<string, bool>();
 
@@ -62,7 +62,7 @@ public async Task CheckRequestedContentTypeAsync(HttpContext httpContext)
                     throw new NotAcceptableException(Api.Resources.UnsupportedFormatParameter);
                 }
 
-                string closestClientMediaType = _outputFormatters.GetClosestClientMediaType(resourceFormat.ToContentType(), acceptHeaders?.Select(x => x.MediaType.Value));
+                string closestClientMediaType = _outputFormatters.GetClosestClientMediaType(resourceFormat.ToContentType(), acceptHeaders?.Select(x => x.MediaType.Value)?.ToList());
 
                 // Overrides output format type
                 httpContext.Response.ContentType = closestClientMediaType;
diff --git a/src/Microsoft.Health.Fhir.Shared.Api/Features/Resources/Bundle/BundleHandler.cs b/src/Microsoft.Health.Fhir.Shared.Api/Features/Resources/Bundle/BundleHandler.cs
index ab0d773a82..e3f273e63d 100644
--- a/src/Microsoft.Health.Fhir.Shared.Api/Features/Resources/Bundle/BundleHandler.cs
+++ b/src/Microsoft.Health.Fhir.Shared.Api/Features/Resources/Bundle/BundleHandler.cs
@@ -845,7 +845,7 @@ private static void SetupContexts(
             }
         }
 
-        private void PopulateReferenceIdDictionary(IEnumerable<EntryComponent> bundleEntries, IDictionary<string, (string resourceId, string resourceType)> idDictionary)
+        private void PopulateReferenceIdDictionary(IReadOnlyCollection<EntryComponent> bundleEntries, IDictionary<string, (string resourceId, string resourceType)> idDictionary)
         {
             foreach (EntryComponent entry in bundleEntries)
             {
diff --git a/src/Microsoft.Health.Fhir.Shared.Core/Features/Validation/ServerProvideProfileValidation.cs b/src/Microsoft.Health.Fhir.Shared.Core/Features/Validation/ServerProvideProfileValidation.cs
index ea6d937248..e5e887f1f3 100644
--- a/src/Microsoft.Health.Fhir.Shared.Core/Features/Validation/ServerProvideProfileValidation.cs
+++ b/src/Microsoft.Health.Fhir.Shared.Core/Features/Validation/ServerProvideProfileValidation.cs
@@ -189,7 +189,7 @@ public IEnumerable<string> GetSupportedProfiles(string resourceType, bool disabl
                 .Select(x => x.ResourceUri).ToList();
         }
 
-        private static string GetHashForSupportedProfiles(IEnumerable<ArtifactSummary> summaries)
+        private static string GetHashForSupportedProfiles(IReadOnlyCollection<ArtifactSummary> summaries)
         {
             if (summaries == null)
             {
diff --git a/src/Microsoft.Health.Fhir.SqlServer/Features/Operations/Import/ImportOrchestratorJob.cs b/src/Microsoft.Health.Fhir.SqlServer/Features/Operations/Import/ImportOrchestratorJob.cs
index 0894609bbb..db10d50996 100644
--- a/src/Microsoft.Health.Fhir.SqlServer/Features/Operations/Import/ImportOrchestratorJob.cs
+++ b/src/Microsoft.Health.Fhir.SqlServer/Features/Operations/Import/ImportOrchestratorJob.cs
@@ -257,7 +257,7 @@ internal static IEnumerable<long> GetOffsets(long blobLength, int bytesToRead)
             }
         }
 
-        private async Task<IList<long>> EnqueueProcessingJobsAsync(IEnumerable<InputResource> inputs, long groupId, ImportOrchestratorJobDefinition coordDefinition, CancellationToken cancellationToken)
+        private async Task<IList<long>> EnqueueProcessingJobsAsync(IReadOnlyCollection<InputResource> inputs, long groupId, ImportOrchestratorJobDefinition coordDefinition, CancellationToken cancellationToken)
         {
             var definitions = new List<ImportProcessingJobDefinition>();
             foreach (var input in inputs.OrderBy(_ => RandomNumberGenerator.GetInt32((int)1e9)))
diff --git a/src/Microsoft.Health.Fhir.SqlServer/Features/Storage/SqlServerFhirDataStore.cs b/src/Microsoft.Health.Fhir.SqlServer/Features/Storage/SqlServerFhirDataStore.cs
index 72b116da30..d4ab819035 100644
--- a/src/Microsoft.Health.Fhir.SqlServer/Features/Storage/SqlServerFhirDataStore.cs
+++ b/src/Microsoft.Health.Fhir.SqlServer/Features/Storage/SqlServerFhirDataStore.cs
@@ -426,11 +426,11 @@ internal async Task<IReadOnlyList<string>> ImportResourcesAsync(IReadOnlyList<Im
                 }
             }
 
-            var dups = resources.Except(results.Loaded).Except(results.Conflicts);
+            var dups = resources.Except(results.Loaded).Except(results.Conflicts)?.ToList();
 
             return GetErrors(dups, results.Conflicts);
 
-            List<string> GetErrors(IEnumerable<ImportResource> dups, IEnumerable<ImportResource> conflicts)
+            List<string> GetErrors(IReadOnlyCollection<ImportResource> dups, IReadOnlyCollection<ImportResource> conflicts)
             {
                 var errors = new List<string>();
                 foreach (var resource in dups)
diff --git a/tools/Exporter/Program.cs b/tools/Exporter/Program.cs
index cef9dfa0bd..58f8f02c66 100644
--- a/tools/Exporter/Program.cs
+++ b/tools/Exporter/Program.cs
@@ -209,7 +209,7 @@ private static int Export(short resourceTypeId, BlobContainerClient container, l
             return strings.Count;
         }
 
-        private static void WriteBatchOfLines(BlobContainerClient container, IEnumerable<string> batch, string blobName)
+        private static void WriteBatchOfLines(BlobContainerClient container, IReadOnlyCollection<string> batch, string blobName)
         {
         retry:
             try
diff --git a/tools/PerfTester/Program.cs b/tools/PerfTester/Program.cs
index 8f9000ccc8..1c010f569c 100644
--- a/tools/PerfTester/Program.cs
+++ b/tools/PerfTester/Program.cs
@@ -309,7 +309,7 @@ private static void ExecuteParallelCalls(ReadOnlyList<(short ResourceTypeId, str
                     }
                     else if (_callType.StartsWith("SearchByIds"))
                     {
-                        var status = GetResources(_nameFilter, resourceIds.Item2.Select(_ => _.ResourceId));
+                        var status = GetResources(_nameFilter, resourceIds.Item2.Select(_ => _.ResourceId)?.ToList());
                         if (status != "OK")
                         {
                             Interlocked.Increment(ref errors);
@@ -793,7 +793,7 @@ private static string PostBundle(string jsonString, string resourceType, string
             return status;
         }
 
-        private static string GetResources(string resourceType, IEnumerable<string> resourceIds)
+        private static string GetResources(string resourceType, System.Collections.Generic.IReadOnlyCollection<string> resourceIds)
         {
             var maxRetries = 3;
             var retries = 0;