diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index c4f0bcd6cc7f..0d31903dc043 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2006-10-29  Roger Sayle  <roger@eyesopen.com>
+
+	* builtins.c (fold_builtin_floor): Check for the availability of
+	the C99 trunc function before transforming floor into trunc.
+
 2006-10-29  Kaveh R. Ghazi  <ghazi@caip.rutgers.edu>
 
 	* builtins.c (fold_builtin_hypot): Rearrange recursive
diff --git a/gcc/builtins.c b/gcc/builtins.c
index 3af86cc10581..b3e82d5d187a 100644
--- a/gcc/builtins.c
+++ b/gcc/builtins.c
@@ -7311,9 +7311,11 @@ fold_builtin_floor (tree fndecl, tree arglist)
 
   /* Fold floor (x) where x is nonnegative to trunc (x).  */
   if (tree_expr_nonnegative_p (arg))
-    return build_function_call_expr (mathfn_built_in (TREE_TYPE (arg),
-						      BUILT_IN_TRUNC),
-				     arglist);
+    {
+      tree truncfn = mathfn_built_in (TREE_TYPE (arg), BUILT_IN_TRUNC);
+      if (truncfn)
+	return build_function_call_expr (truncfn, arglist);
+    }
 
   return fold_trunc_transparent_mathfn (fndecl, arglist);
 }