diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Converters.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Converters.cs
index 91264247bc9539..478029174db339 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Converters.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Converters.cs
@@ -9,6 +9,7 @@
 using System.Text.Json.Serialization;
 using System.Text.Json.Serialization.Converters;
 using System.Text.Json.Serialization.Metadata;
+using System.Threading;
 
 namespace System.Text.Json
 {
@@ -29,11 +30,14 @@ public sealed partial class JsonSerializerOptions
         [RequiresUnreferencedCode(JsonSerializer.SerializationUnreferencedCodeMessage)]
         private static void RootReflectionSerializerDependencies()
         {
-            if (s_defaultSimpleConverters is null)
+            // s_typeInfoCreationFunc is the last field assigned.
+            // Use it as the sentinel to ensure that all dependencies are initialized.
+            if (Volatile.Read(ref s_typeInfoCreationFunc) is null)
             {
                 s_defaultSimpleConverters = GetDefaultSimpleConverters();
                 s_defaultFactoryConverters = GetDefaultFactoryConverters();
-                s_typeInfoCreationFunc = CreateJsonTypeInfo;
+                // Explicitly ensure that the previous fields are initialized along with this one.
+                Volatile.Write(ref s_typeInfoCreationFunc, CreateJsonTypeInfo);
             }
 
             [RequiresUnreferencedCode(JsonSerializer.SerializationUnreferencedCodeMessage)]
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.cs
index 95199d7ead9c54..8837b55dcf5da5 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.cs
@@ -9,6 +9,7 @@
 using System.Text.Json.Nodes;
 using System.Text.Json.Serialization;
 using System.Text.Json.Serialization.Metadata;
+using System.Threading;
 
 namespace System.Text.Json
 {
@@ -579,7 +580,7 @@ internal MemberAccessor MemberAccessorStrategy
         /// <summary>
         /// Whether the options instance has been primed for reflection-based serialization.
         /// </summary>
-        internal bool IsInitializedForReflectionSerializer { get; private set; }
+        internal bool IsInitializedForReflectionSerializer;
 
         /// <summary>
         /// Initializes the converters for the reflection-based serializer.
@@ -589,7 +590,7 @@ internal MemberAccessor MemberAccessorStrategy
         internal void InitializeForReflectionSerializer()
         {
             RootReflectionSerializerDependencies();
-            IsInitializedForReflectionSerializer = true;
+            Volatile.Write(ref IsInitializedForReflectionSerializer, true);
             if (_cachingContext != null)
             {
                 _cachingContext.Options.IsInitializedForReflectionSerializer = true;
@@ -610,7 +611,9 @@ private JsonTypeInfo GetJsonTypeInfoFromContextOrCreate(Type type)
                 return null!;
             }
 
-            Debug.Assert(s_typeInfoCreationFunc != null);
+            Debug.Assert(
+                s_typeInfoCreationFunc != null,
+                "Reflection-based JsonTypeInfo creator should be initialized if IsInitializedForReflectionSerializer is true.");
             return s_typeInfoCreationFunc(type, this);
         }