diff --git a/src/libraries/System.Composition.TypedParts/src/System/Composition/TypedParts/Discovery/DiscoveredPart.cs b/src/libraries/System.Composition.TypedParts/src/System/Composition/TypedParts/Discovery/DiscoveredPart.cs
index 88f005d09ed1e4..5f8e9d05b1264d 100644
--- a/src/libraries/System.Composition.TypedParts/src/System/Composition/TypedParts/Discovery/DiscoveredPart.cs
+++ b/src/libraries/System.Composition.TypedParts/src/System/Composition/TypedParts/Discovery/DiscoveredPart.cs
@@ -12,6 +12,7 @@
 using System.Linq.Expressions;
 using System.Numerics.Hashing;
 using System.Reflection;
+using System.Threading;
 
 namespace System.Composition.TypedParts.Discovery
 {
@@ -31,6 +32,7 @@ internal sealed class DiscoveredPart
 
         // Lazily initialised among potentially many exports
         private ConstructorInfo _constructor;
+        private ParameterInfo[] _constructorParameters;
         private CompositeActivator _partActivator;
 
         private static readonly IDictionary<string, object> s_noMetadata = new Dictionary<string, object>();
@@ -112,7 +114,12 @@ private IEnumerable<CompositionDependency> GetPartActivatorDependencies(Dependen
                 }
             }
 
-            var cps = _constructor.GetParameters();
+            // Use LazyInitializer to ensure GetParameters() is called at most once per
+            // DiscoveredPart instance and the result is safely published to all threads.
+            // On some runtimes (e.g. Mono on ARM), concurrent calls to GetParameters()
+            // on the same ConstructorInfo can return different ParameterInfo instances
+            // due to lazy initialization, causing lookup failures in GetActivator.
+            var cps = LazyInitializer.EnsureInitialized(ref _constructorParameters, () => _constructor.GetParameters());
 
             for (var i = 0; i < cps.Length; ++i)
             {
@@ -168,7 +175,7 @@ public CompositeActivator GetActivator(IEnumerable<CompositionDependency> depend
             var contextParam = Expression.Parameter(typeof(LifetimeContext), "cc");
             var operationParm = Expression.Parameter(typeof(CompositionOperation), "op");
 
-            var cps = _constructor.GetParameters();
+            var cps = LazyInitializer.EnsureInitialized(ref _constructorParameters, _constructor.GetParameters);
             Expression[] paramActivatorCalls = new Expression[cps.Length];
 
             var partActivatorDependencies = dependencies