Index: internal.h
===================================================================
--- internal.h	(revision 55820)
+++ internal.h	(working copy)
@@ -983,8 +983,18 @@
     VALUE klass;
 };
 
-#define RBASIC_CLEAR_CLASS(obj)        (((struct RBasicRaw *)((VALUE)(obj)))->klass = 0)
-#define RBASIC_SET_CLASS_RAW(obj, cls) (((struct RBasicRaw *)((VALUE)(obj)))->klass = (cls))
+#ifdef __ibmxl__
+    #define RBASIC_SET_CLASS_RAW(obj, cls) memcpy(&((struct RBasicRaw *)((VALUE)(obj)))->klass, &(cls), sizeof(VALUE))
+#else
+    #define RBASIC_SET_CLASS_RAW(obj, cls) (((struct RBasicRaw *)((VALUE)(obj)))->klass = (cls))
+#endif
+
+#ifdef __ibmxl__
+    #define RBASIC_CLEAR_CLASS(obj)        memset(&(((struct RBasicRaw *)((VALUE)(obj)))->klass), 0, sizeof(((struct RBasicRaw *)((VALUE)(obj)))->klass))
+#else
+    #define RBASIC_CLEAR_CLASS(obj)        (((struct RBasicRaw *)((VALUE)(obj)))->klass = 0)
+#endif
+
 #define RBASIC_SET_CLASS(obj, cls)     do { \
     VALUE _obj_ = (obj); \
     RB_OBJ_WRITE(_obj_, &((struct RBasicRaw *)(_obj_))->klass, cls); \