diff --git a/xo-reader/src/reader/progress_xs.cpp b/xo-reader/src/reader/progress_xs.cpp
index 99328d71..2c94733a 100644
--- a/xo-reader/src/reader/progress_xs.cpp
+++ b/xo-reader/src/reader/progress_xs.cpp
@@ -192,7 +192,14 @@ namespace xo {
                 break;
 
             case optype::op_not_equal:
-                assert(false);
+                if (lhs_->valuetype()->is_i64() && rhs_->valuetype()->is_i64()) {
+                    return Apply::make_cmp_ne_i64(lhs_, rhs_);
+                } else {
+                    this->apply_type_error(c_self_name,
+                                           op_type_, lhs_, rhs_, p_psm);
+                    return nullptr;
+                }
+                break;
 
             case optype::op_less:
                 // TODO: floating-point less-than