diff --git a/internal/class.h b/internal/class.h
index 296a07ae29..ea68b07fc2 100644
--- a/internal/class.h
+++ b/internal/class.h
@@ -658,8 +658,8 @@ RCLASS_SET_REFINED_CLASS(VALUE klass, VALUE refined)
 static inline rb_alloc_func_t
 RCLASS_ALLOCATOR(VALUE klass)
 {
-    RUBY_ASSERT(RB_TYPE_P(klass, T_CLASS) || RB_TYPE_P(klass, T_ICLASS));
-    if (RCLASS_SINGLETON_P(klass) || RB_TYPE_P(klass, T_ICLASS)) {
+    RBIMPL_ASSERT_TYPE(klass, T_CLASS);
+    if (RCLASS_SINGLETON_P(klass)) {
         return 0;
     }
     return RCLASS_EXT_PRIME(klass)->as.class.allocator;
diff --git a/vm_method.c b/vm_method.c
index dbc5ad97ed..17f68fc258 100644
--- a/vm_method.c
+++ b/vm_method.c
@@ -1635,10 +1635,20 @@ rb_undef_alloc_func(VALUE klass)
 rb_alloc_func_t
 rb_get_alloc_func(VALUE klass)
 {
-    Check_Type(klass, T_CLASS);
+    RBIMPL_ASSERT_TYPE(klass, T_CLASS);
 
-    for (; klass; klass = RCLASS_SUPER(klass)) {
-        rb_alloc_func_t allocator = RCLASS_ALLOCATOR(klass);
+    rb_alloc_func_t allocator = RCLASS_ALLOCATOR(klass);
+    if (allocator == UNDEF_ALLOC_FUNC) return 0;
+    if (allocator) return allocator;
+
+    VALUE *superclasses = RCLASS_SUPERCLASSES(klass);
+    size_t depth = RCLASS_SUPERCLASS_DEPTH(klass);
+
+    for (size_t i = depth; i > 0; i--) {
+        klass = superclasses[i - 1];
+        RBIMPL_ASSERT_TYPE(klass, T_CLASS);
+
+        allocator = RCLASS_ALLOCATOR(klass);
         if (allocator == UNDEF_ALLOC_FUNC) break;
         if (allocator) return allocator;
     }