diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Nodes/JsonObject.IDictionary.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Nodes/JsonObject.IDictionary.cs
index 8756b93366f90..3de8d933a1b07 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Nodes/JsonObject.IDictionary.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Nodes/JsonObject.IDictionary.cs
@@ -25,6 +25,11 @@ public partial class JsonObject : IDictionary<string, JsonNode?>
         /// </exception>
         public void Add(string propertyName, JsonNode? value)
         {
+            if (propertyName is null)
+            {
+                ThrowHelper.ThrowArgumentNullException(nameof(propertyName));
+            }
+
             Dictionary.Add(propertyName, value);
             value?.AssignParent(this);
         }
@@ -74,7 +79,15 @@ public void Clear()
         /// <exception cref="ArgumentNullException">
         ///   <paramref name="propertyName"/> is <see langword="null"/>.
         /// </exception>
-        public bool ContainsKey(string propertyName) => Dictionary.ContainsKey(propertyName);
+        public bool ContainsKey(string propertyName)
+        {
+            if (propertyName is null)
+            {
+                ThrowHelper.ThrowArgumentNullException(nameof(propertyName));
+            }
+
+            return Dictionary.ContainsKey(propertyName);
+        }
 
         /// <summary>
         ///   Gets the number of elements contained in <see cref="JsonObject"/>.
@@ -180,7 +193,15 @@ public bool Remove(string propertyName)
         /// <exception cref="ArgumentNullException">
         ///   <paramref name="propertyName"/> is <see langword="null"/>.
         /// </exception>
-        bool IDictionary<string, JsonNode?>.TryGetValue(string propertyName, out JsonNode? jsonNode) => Dictionary.TryGetValue(propertyName, out jsonNode);
+        bool IDictionary<string, JsonNode?>.TryGetValue(string propertyName, out JsonNode? jsonNode)
+        {
+            if (propertyName is null)
+            {
+                ThrowHelper.ThrowArgumentNullException(nameof(propertyName));
+            }
+
+            return Dictionary.TryGetValue(propertyName, out jsonNode);
+        }
 
         /// <summary>
         ///   Returns <see langword="false"/>.
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Nodes/JsonObject.IList.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Nodes/JsonObject.IList.cs
index d7032fd5125ed..372eccdcfe016 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Nodes/JsonObject.IList.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Nodes/JsonObject.IList.cs
@@ -23,6 +23,11 @@ public partial class JsonObject : IList<KeyValuePair<string, JsonNode?>>
         /// <exception cref="InvalidOperationException"><paramref name="value"/> already has a parent.</exception>
         public void SetAt(int index, string propertyName, JsonNode? value)
         {
+            if (propertyName is null)
+            {
+                ThrowHelper.ThrowArgumentNullException(nameof(propertyName));
+            }
+
             OrderedDictionary<string, JsonNode?> dictionary = Dictionary;
             KeyValuePair<string, JsonNode?> existing = dictionary.GetAt(index);
             dictionary.SetAt(index, propertyName, value);
@@ -48,7 +53,15 @@ public void SetAt(int index, JsonNode? value)
         /// <param name="propertyName">The property name to locate.</param>
         /// <returns>The index of <paramref name="propertyName"/> if found; otherwise, -1.</returns>
         /// <exception cref="ArgumentNullException"><paramref name="propertyName"/> is null.</exception>
-        public int IndexOf(string propertyName) => Dictionary.IndexOf(propertyName);
+        public int IndexOf(string propertyName)
+        {
+            if (propertyName is null)
+            {
+                ThrowHelper.ThrowArgumentNullException(nameof(propertyName));
+            }
+
+            return Dictionary.IndexOf(propertyName);
+        }
 
         /// <summary>Inserts a property into the object at the specified index.</summary>
         /// <param name="index">The zero-based index at which the property should be inserted.</param>
@@ -59,6 +72,11 @@ public void SetAt(int index, JsonNode? value)
         /// <exception cref="ArgumentOutOfRangeException"><paramref name="index"/> is less than 0 or greater than <see cref="Count"/>.</exception>
         public void Insert(int index, string propertyName, JsonNode? value)
         {
+            if (propertyName is null)
+            {
+                ThrowHelper.ThrowArgumentNullException(nameof(propertyName));
+            }
+
             Dictionary.Insert(index, propertyName, value);
             value?.AssignParent(this);
         }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Nodes/JsonObject.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Nodes/JsonObject.cs
index 8b32efee897e2..62dcaf2fee8c7 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Nodes/JsonObject.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Nodes/JsonObject.cs
@@ -116,8 +116,15 @@ internal string GetPropertyName(JsonNode? node)
         /// <returns>
         ///   <see langword="true"/> if a property with the specified name was found; otherwise, <see langword="false"/>.
         /// </returns>
-        public bool TryGetPropertyValue(string propertyName, out JsonNode? jsonNode) =>
-            Dictionary.TryGetValue(propertyName, out jsonNode);
+        public bool TryGetPropertyValue(string propertyName, out JsonNode? jsonNode)
+        {
+            if (propertyName is null)
+            {
+                ThrowHelper.ThrowArgumentNullException(nameof(propertyName));
+            }
+
+            return Dictionary.TryGetValue(propertyName, out jsonNode);
+        }
 
         /// <inheritdoc/>
         public override void WriteTo(Utf8JsonWriter writer, JsonSerializerOptions? options = null)