diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index bfa8e954ee8..8288483e5c4 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2002-06-11  Tom Tromey  <tromey@redhat.com>
+
+	For PR java/6520:
+	* fold-const.c (fold_convert): Don't modify existing tree's type.
+
 2002-06-11  Geoffrey Keating  <geoffk@redhat.com>
 
 	* config/rs6000/ppc-asm.h: Remove some Windows NT leftovers.
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index db415649f0f..1c29ad57fbf 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -1596,8 +1596,10 @@ fold_convert (t, arg1)
 	{
 	  if (REAL_VALUE_ISNAN (TREE_REAL_CST (arg1)))
 	    {
-	      t = arg1;
-	      TREE_TYPE (arg1) = type;
+	      /* We make a copy of ARG1 so that we don't modify an
+		 existing constant tree.  */
+	      t = copy_node (arg1);
+	      TREE_TYPE (t) = type;
 	      return t;
 	    }