diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index e8eb55880b7..bf6cf528f20 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2004-12-09  Richard Henderson  <rth@redhat.com>
+
+	PR c/18282
+	* attribs.c (decl_attributes): Use relayout_decl.
+	* c-common.c (handle_mode_attribute): Copy all relevant type
+	parameters from the new underlying integral type.
+
 2004-12-09  Richard Henderson  <rth@redhat.com>
 
 	* c-common.c (shorten_compare): Don't special-case min/maxval
diff --git a/gcc/attribs.c b/gcc/attribs.c
index 1aab101c624..fd11a96700f 100644
--- a/gcc/attribs.c
+++ b/gcc/attribs.c
@@ -259,13 +259,7 @@ decl_attributes (tree *node, tree attributes, int flags)
 	  && (TREE_CODE (*node) == VAR_DECL
 	      || TREE_CODE (*node) == PARM_DECL
 	      || TREE_CODE (*node) == RESULT_DECL))
-	{
-	  /* Force a recalculation of mode and size.  */
-	  DECL_MODE (*node) = VOIDmode;
-	  DECL_SIZE (*node) = 0;
-
-	  layout_decl (*node, 0);
-	}
+	relayout_decl (*node);
 
       if (!no_add_attrs)
 	{
diff --git a/gcc/c-common.c b/gcc/c-common.c
index fa555a72588..d58d326b5f4 100644
--- a/gcc/c-common.c
+++ b/gcc/c-common.c
@@ -4302,7 +4302,17 @@ handle_mode_attribute (tree *node, tree name, tree args,
 
 	  if (!(flags & (int) ATTR_FLAG_TYPE_IN_PLACE))
 	    type = build_variant_type_copy (type);
+
+	  /* We cannot use layout_type here, because that will attempt
+	     to re-layout all variants, corrupting our original.  */
 	  TYPE_PRECISION (type) = TYPE_PRECISION (typefm);
+	  TYPE_MIN_VALUE (type) = TYPE_MIN_VALUE (typefm);
+	  TYPE_MAX_VALUE (type) = TYPE_MAX_VALUE (typefm);
+	  TYPE_SIZE (type) = TYPE_SIZE (typefm);
+	  TYPE_SIZE_UNIT (type) = TYPE_SIZE_UNIT (typefm);
+	  if (!TYPE_USER_ALIGN (type))
+	    TYPE_ALIGN (type) = TYPE_ALIGN (typefm);
+
 	  typefm = type;
 	}
       else if (VECTOR_MODE_P (mode)
@@ -4314,8 +4324,6 @@ handle_mode_attribute (tree *node, tree name, tree args,
 	}
 
       *node = typefm;
-
-      /* No need to layout the type here.  The caller should do this.  */
     }
 
   return NULL_TREE;