diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 5e485f10d19..ea530ef36f4 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -19770,6 +19770,8 @@ tsubst_copy_and_build (tree t,
 				complain|decltype_flag));
 
     case FIX_TRUNC_EXPR:
+    case FLOAT_EXPR:
+      /* convert_like should have created an IMPLICIT_CONV_EXPR.  */
       gcc_unreachable ();
 
     case ADDR_EXPR: