diff --git a/src/share/vm/oops/klass.hpp b/src/share/vm/oops/klass.hpp
index 1ca027a3762d30f268ae3cd7e9ba76aee6023b0c..00b208b4ed0ce496e6a723438c4c97a679800f3d 100644
--- a/src/share/vm/oops/klass.hpp
+++ b/src/share/vm/oops/klass.hpp
@@ -352,7 +352,8 @@ class Klass : public Metadata {
   static int layout_helper_log2_element_size(jint lh) {
     assert(lh < (jint)_lh_neutral_value, "must be array");
     int l2esz = (lh >> _lh_log2_element_size_shift) & _lh_log2_element_size_mask;
-    assert(l2esz <= LogBitsPerLong, "sanity");
+    assert(l2esz <= LogBitsPerLong,
+        err_msg("sanity. l2esz: 0x%x for lh: 0x%x", (uint)l2esz, (uint)lh));
     return l2esz;
   }
   static jint array_layout_helper(jint tag, int hsize, BasicType etype, int log2_esize) {