diff --git a/src/Peachpie.Library/Reflection/ReflectionUtils.cs b/src/Peachpie.Library/Reflection/ReflectionUtils.cs
index 11df12801b..83908131ed 100644
--- a/src/Peachpie.Library/Reflection/ReflectionUtils.cs
+++ b/src/Peachpie.Library/Reflection/ReflectionUtils.cs
@@ -57,7 +57,7 @@ public static List<ReflectionParameter> ResolveReflectionParameters(ReflectionFu
                 {
                     var p = ps[pi];
 
-                    var allowsNull = p.GetCustomAttribute<NotNullAttribute>() == null;
+                    var allowsNull = p.IsNullable();
                     var defaultValue = p.HasDefaultValue ? PhpValue.FromClr(p.RawDefaultValue) : default(PhpValue);
                     var isVariadic = p.GetCustomAttribute<ParamArrayAttribute>() != null;
 
diff --git a/src/Peachpie.Runtime/Reflection/ReflectionUtils.cs b/src/Peachpie.Runtime/Reflection/ReflectionUtils.cs
index c4aaa58cf7..d16c260d90 100644
--- a/src/Peachpie.Runtime/Reflection/ReflectionUtils.cs
+++ b/src/Peachpie.Runtime/Reflection/ReflectionUtils.cs
@@ -88,6 +88,31 @@ public static bool IsPhpClassType(TypeInfo tinfo)
             return !tinfo.IsValueType && t != typeof(PhpArray) && t != typeof(string) && t != typeof(IPhpCallable);
         }
 
+        /// <summary>
+        /// Determines whether given parametr allows <c>NULL</c> as the argument value.
+        /// </summary>
+        public static bool IsNullable(this ParameterInfo p)
+        {
+            if (p.ParameterType.IsValueType &&
+                p.ParameterType != typeof(PhpValue) &&
+                //p.ParameterType != typeof(PhpArray) // TODO: uncomment when PhpArray will be struct
+                p.ParameterType != typeof(PhpString))
+            {
+                if (p.ParameterType.IsNullable_T(out var _))
+                {
+                    return true;
+                }
+
+                // NULL is not possible on value types
+                return false;
+            }
+            else
+            {
+                // NULL is explicitly disallowed?
+                return p.GetCustomAttribute<NotNullAttribute>() == null;
+            }
+        }
+
         /// <summary>
         /// Types that we do not expose in reflection.
         /// </summary>