diff --git a/src/ast/rewriter/seq_rewriter.cpp b/src/ast/rewriter/seq_rewriter.cpp
index 533d9f09f..fc38f0ae4 100644
--- a/src/ast/rewriter/seq_rewriter.cpp
+++ b/src/ast/rewriter/seq_rewriter.cpp
@@ -1103,7 +1103,7 @@ br_status seq_rewriter::mk_str_stoi(expr* a, expr_ref& result) {
     }
     expr* b;
     if (m_util.str.is_itos(a, b)) {
-        result = b;
+        result = m().mk_ite(m_autil.mk_ge(b, m_autil.mk_int(0)), b, m_autil.mk_int(-1));
         return BR_DONE;
     }
     return BR_FAILED;