diff --git a/src/Bicep.Core.IntegrationTests/ScenarioTests.cs b/src/Bicep.Core.IntegrationTests/ScenarioTests.cs
index 830acf0d870..11c60b203bf 100644
--- a/src/Bicep.Core.IntegrationTests/ScenarioTests.cs
+++ b/src/Bicep.Core.IntegrationTests/ScenarioTests.cs
@@ -4955,6 +4955,19 @@ public void Test_Issue502()
             ("BCP353", DiagnosticLevel.Error, "The types \"foo\", \"FoO\" differ only in casing. The ARM deployments engine is not case sensitive and will not be able to distinguish between them."),
         });
 
+        result = CompilationHelper.Compile(Services.WithFeatureOverrides(new(UserDefinedTypesEnabled: true)), """
+            param x {
+              foo: string
+              FoO: int
+            }
+            """);
+
+        result.ExcludingLinterDiagnostics().Should().HaveDiagnostics(new[]
+        {
+            ("BCP353", DiagnosticLevel.Error, "The type properties \"foo\", \"FoO\" differ only in casing. The ARM deployments engine is not case sensitive and will not be able to distinguish between them."),
+            ("BCP353", DiagnosticLevel.Error, "The type properties \"foo\", \"FoO\" differ only in casing. The ARM deployments engine is not case sensitive and will not be able to distinguish between them."),
+        });
+
         result = CompilationHelper.Compile(Services.WithFeatureOverrides(new(AssertsEnabled: true)), """
             assert foo = true
             assert FoO = true
diff --git a/src/Bicep.Core/Diagnostics/DiagnosticBuilder.cs b/src/Bicep.Core/Diagnostics/DiagnosticBuilder.cs
index 18a46f7ee4d..bd0e812c535 100644
--- a/src/Bicep.Core/Diagnostics/DiagnosticBuilder.cs
+++ b/src/Bicep.Core/Diagnostics/DiagnosticBuilder.cs
@@ -1981,10 +1981,10 @@ public ErrorDiagnostic RuntimeValueNotAllowedInFunctionDeclaration(string? acces
                 "BCP352",
                 $"Failed to evaluate variable \"{name}\": {message}");
 
-            public ErrorDiagnostic SymbolsMustBeCaseInsensitivelyUnique(string symbolTypePluralName, IEnumerable<string> symbolNames) => new(
+            public ErrorDiagnostic ItemsMustBeCaseInsensitivelyUnique(string itemTypePluralName, IEnumerable<string> itemNames) => new(
                 TextSpan,
                 "BCP353",
-                $"The {symbolTypePluralName} {ToQuotedString(symbolNames)} differ only in casing. The ARM deployments engine is not case sensitive and will not be able to distinguish between them.");
+                $"The {itemTypePluralName} {ToQuotedString(itemNames)} differ only in casing. The ARM deployments engine is not case sensitive and will not be able to distinguish between them.");
         }
 
         public static DiagnosticBuilderInternal ForPosition(TextSpan span)
diff --git a/src/Bicep.Core/Emit/EmitLimitationCalculator.cs b/src/Bicep.Core/Emit/EmitLimitationCalculator.cs
index a9eb50fd5eb..4a73d325764 100644
--- a/src/Bicep.Core/Emit/EmitLimitationCalculator.cs
+++ b/src/Bicep.Core/Emit/EmitLimitationCalculator.cs
@@ -7,14 +7,15 @@
 using System.Linq;
 using Bicep.Core.DataFlow;
 using Bicep.Core.Diagnostics;
+using Bicep.Core.Extensions;
+using Bicep.Core.Parsing;
 using Bicep.Core.Semantics;
 using Bicep.Core.Semantics.Metadata;
 using Bicep.Core.Syntax;
+using Bicep.Core.Syntax.Visitors;
 using Bicep.Core.TypeSystem;
 using Bicep.Core.TypeSystem.Az;
 using Bicep.Core.Utils;
-using Bicep.Core.Extensions;
-using Bicep.Core.Syntax.Visitors;
 using Microsoft.WindowsAzure.ResourceStack.Common.Extensions;
 using Newtonsoft.Json.Linq;
 
@@ -603,24 +604,33 @@ private static void BlockNamesDistinguishedOnlyByCase(SemanticModel model, IDiag
                 ("asserts", model.Root.AssertDeclarations),
             })
             {
-                BlockCaseInsensitiveNameClashes(symbolTypePluralName, symbolsOfType, diagnostics);
+                BlockCaseInsensitiveNameClashes(symbolTypePluralName, symbolsOfType, s => s.Name, s => s.NameSource, diagnostics);
+            }
+
+            foreach (var objectTypeDeclaration in SyntaxAggregator.AggregateByType<ObjectTypeSyntax>(model.SourceFile.ProgramSyntax))
+            {
+                BlockCaseInsensitiveNameClashes("type properties",
+                    objectTypeDeclaration.Properties.SelectMany(p => p.TryGetKeyText() is string key ? (key, p.Key).AsEnumerable() : Enumerable.Empty<(string, SyntaxBase)>()),
+                    t => t.Item1,
+                    t => t.Item2,
+                    diagnostics);
             }
         }
 
-        private static void BlockCaseInsensitiveNameClashes(string symbolTypePluralName, IEnumerable<DeclaredSymbol> symbolsOfType, IDiagnosticWriter diagnostics)
+        private static void BlockCaseInsensitiveNameClashes<T>(string itemTypePluralName, IEnumerable<T> itemsOfType, Func<T, string> nameExtractor, Func<T, IPositionable> nameSyntaxExtractor, IDiagnosticWriter diagnostics)
         {
-            foreach (var grouping in symbolsOfType.ToLookup(s => s.Name, StringComparer.OrdinalIgnoreCase).Where(g => g.Count() > 1))
+            foreach (var grouping in itemsOfType.ToLookup(nameExtractor, StringComparer.OrdinalIgnoreCase).Where(g => g.Count() > 1))
             {
-                var clashingSymbols = grouping.Select(s => s.Name).ToArray();
+                var clashingNames = grouping.Select(nameExtractor).ToArray();
 
                 // if any symbols are exact matches, a different diagnostic about multiple declarations will have already been raised
-                if (clashingSymbols.Distinct().Count() != clashingSymbols.Length)
+                if (clashingNames.Distinct().Count() != clashingNames.Length)
                 {
                     continue;
                 }
 
                 diagnostics.WriteMultiple(grouping.Select(
-                    symbol => DiagnosticBuilder.ForPosition(symbol.NameSource).SymbolsMustBeCaseInsensitivelyUnique(symbolTypePluralName, clashingSymbols)));
+                    item => DiagnosticBuilder.ForPosition(nameSyntaxExtractor(item)).ItemsMustBeCaseInsensitivelyUnique(itemTypePluralName, clashingNames)));
             }
         }
     }