diff --git a/agent/src/share/classes/sun/jvm/hotspot/oops/InstanceKlass.java b/agent/src/share/classes/sun/jvm/hotspot/oops/InstanceKlass.java
index 7052f8a2d18c2597305b77b331b8322fec3373d6..cfa26eacdbd4eb16dafc11de057e5dd368183dca 100644
--- a/agent/src/share/classes/sun/jvm/hotspot/oops/InstanceKlass.java
+++ b/agent/src/share/classes/sun/jvm/hotspot/oops/InstanceKlass.java
@@ -53,6 +53,7 @@ public class InstanceKlass extends Klass {
   private static int HIGH_OFFSET;
   private static int FIELD_SLOTS;
   private static short FIELDINFO_TAG_SIZE;
+  private static short FIELDINFO_TAG_MASK;
   private static short FIELDINFO_TAG_OFFSET;
 
   // ClassState constants
@@ -102,6 +103,7 @@ public class InstanceKlass extends Klass {
     HIGH_OFFSET                    = db.lookupIntConstant("FieldInfo::high_packed_offset").intValue();
     FIELD_SLOTS                    = db.lookupIntConstant("FieldInfo::field_slots").intValue();
     FIELDINFO_TAG_SIZE             = db.lookupIntConstant("FIELDINFO_TAG_SIZE").shortValue();
+    FIELDINFO_TAG_MASK             = db.lookupIntConstant("FIELDINFO_TAG_MASK").shortValue();
     FIELDINFO_TAG_OFFSET           = db.lookupIntConstant("FIELDINFO_TAG_OFFSET").shortValue();
 
     // read ClassState constants
@@ -321,7 +323,7 @@ public class InstanceKlass extends Klass {
     U2Array fields = getFields();
     short lo = fields.at(index * FIELD_SLOTS + LOW_OFFSET);
     short hi = fields.at(index * FIELD_SLOTS + HIGH_OFFSET);
-    if ((lo & FIELDINFO_TAG_SIZE) == FIELDINFO_TAG_OFFSET) {
+    if ((lo & FIELDINFO_TAG_MASK) == FIELDINFO_TAG_OFFSET) {
       return VM.getVM().buildIntFromShorts(lo, hi) >> FIELDINFO_TAG_SIZE;
     }
     throw new RuntimeException("should not reach here");
diff --git a/src/share/vm/runtime/vmStructs.cpp b/src/share/vm/runtime/vmStructs.cpp
index e180f7d449fd45236cd98dfd4a4228395bfc0aa7..a1fe3f2aa6371b3c794b3787580233cbc4beefe4 100644
--- a/src/share/vm/runtime/vmStructs.cpp
+++ b/src/share/vm/runtime/vmStructs.cpp
@@ -2291,6 +2291,7 @@ typedef BinaryTreeDictionary<Metablock, FreeList> MetablockTreeDictionary;
   /*************************************/                                 \
                                                                           \
   declare_preprocessor_constant("FIELDINFO_TAG_SIZE", FIELDINFO_TAG_SIZE) \
+  declare_preprocessor_constant("FIELDINFO_TAG_MASK", FIELDINFO_TAG_MASK) \
   declare_preprocessor_constant("FIELDINFO_TAG_OFFSET", FIELDINFO_TAG_OFFSET) \
                                                                           \
   /************************************************/                      \