diff --git a/src/Compilers/Core/Portable/Diagnostic/Diagnostic_SimpleDiagnostic.cs b/src/Compilers/Core/Portable/Diagnostic/Diagnostic_SimpleDiagnostic.cs
index 4d36f6c3db7c7..e5c370a9c0ff1 100644
--- a/src/Compilers/Core/Portable/Diagnostic/Diagnostic_SimpleDiagnostic.cs
+++ b/src/Compilers/Core/Portable/Diagnostic/Diagnostic_SimpleDiagnostic.cs
@@ -34,13 +34,18 @@ private SimpleDiagnostic(
                 if ((warningLevel == 0 && severity != DiagnosticSeverity.Error) ||
                     (warningLevel != 0 && severity == DiagnosticSeverity.Error))
                 {
-                    throw new ArgumentException("warningLevel");
+                    throw new ArgumentException(nameof(warningLevel));
+                }
+
+                if(descriptor == null)
+                {
+                    throw new ArgumentNullException(nameof(descriptor));
                 }
 
                 _descriptor = descriptor;
                 _severity = severity;
                 _warningLevel = warningLevel;
-                _location = location;
+                _location = location ?? Location.None;
                 _additionalLocations = additionalLocations == null ? SpecializedCollections.EmptyReadOnlyList<Location>() : additionalLocations.ToImmutableArray();
                 _messageArgs = messageArgs ?? SpecializedCollections.EmptyArray<object>();
             }
@@ -131,10 +136,9 @@ public override bool Equals(object obj)
             public override int GetHashCode()
             {
                 return Hash.Combine(_descriptor,
-                        Hash.Combine(_messageArgs.GetHashCode(),
-                         Hash.Combine(_location.GetHashCode(),
-                          Hash.Combine(_severity.GetHashCode(), _warningLevel)
-                        )));
+                    Hash.CombineValues(_messageArgs,
+                    Hash.Combine(_warningLevel,
+                    Hash.Combine(_location, (int)_severity))));
             }
 
             internal override Diagnostic WithLocation(Location location)
diff --git a/src/Compilers/Core/Portable/InternalUtilities/Hash.cs b/src/Compilers/Core/Portable/InternalUtilities/Hash.cs
index 4dfeff33829be..1bb82411f4323 100644
--- a/src/Compilers/Core/Portable/InternalUtilities/Hash.cs
+++ b/src/Compilers/Core/Portable/InternalUtilities/Hash.cs
@@ -66,6 +66,30 @@ internal static int CombineValues<T>(IEnumerable<T> values, int maxItemsToHash =
             return hashCode;
         }
 
+        internal static int CombineValues<T>(T[] values, int maxItemsToHash = int.MaxValue)
+        {
+            if (values == null)
+            {
+                return 0;
+            }
+
+            var maxSize = Math.Min(maxItemsToHash, values.Length);
+            var hashCode = 0;
+
+            for (int i = 0; i < maxSize; i++)
+            {
+                T value = values[i];
+
+                // Should end up with a constrained virtual call to object.GetHashCode (i.e. avoid boxing where possible).
+                if (value != null)
+                {
+                    hashCode = Hash.Combine(value.GetHashCode(), hashCode);
+                }
+            }
+
+            return hashCode;
+        }
+
         internal static int CombineValues<T>(ImmutableArray<T> values, int maxItemsToHash = int.MaxValue)
         {
             if (values.IsDefaultOrEmpty)