diff --git a/src/ast/rewriter/seq_rewriter.cpp b/src/ast/rewriter/seq_rewriter.cpp
index 49957a01f..30d43105c 100644
--- a/src/ast/rewriter/seq_rewriter.cpp
+++ b/src/ast/rewriter/seq_rewriter.cpp
@@ -1673,6 +1673,37 @@ br_status seq_rewriter::mk_re_concat(expr* a, expr* b, expr_ref& result) {
         result = a;
         return BR_DONE;
     }
+    expr* a1 = nullptr, *b1 = nullptr;
+    if (m_util.re.is_star(a, a1) && m_util.re.is_star(b, b1) && a1 == b1) {
+        result = a;
+        return BR_DONE;
+    }
+    if (m_util.re.is_star(a, a1) && a1 == b) {
+        result = m_util.re.mk_concat(b, a);
+        return BR_DONE;
+    }
+    {
+        unsigned lo1, hi1, lo2, hi2;
+        if (m_util.re.is_loop(a, a1, lo1, hi1) && m_util.re.is_loop(b, b1, lo2, hi2) && a1 == b1) {
+            result = m_util.re.mk_loop(a1, lo1 + lo2, hi1 + hi2);
+            return BR_DONE;
+        }
+        if (m_util.re.is_loop(a, a1, lo1) && m_util.re.is_loop(b, b1, lo2) && a1 == b1) {
+            result = m_util.re.mk_loop(a1, lo1 + lo2);
+            return BR_DONE;
+        }
+    }
+    {
+        expr* lo1, *hi1, *lo2, *hi2;
+        if (m_util.re.is_loop(a, a1, lo1, hi1) && m_util.re.is_loop(b, b1, lo2, hi2) && a1 == b1) {
+            result = m_util.re.mk_loop(a1, m_autil.mk_add(lo1, lo2), m_autil.mk_add(hi1, hi2));
+            return BR_DONE;
+        }
+        if (m_util.re.is_loop(a, a1, lo1) && m_util.re.is_loop(b, b1, lo2) && a1 == b1) {
+            result = m_util.re.mk_loop(a1, m_autil.mk_add(lo1, lo2));
+            return BR_DONE;
+        }
+    }
     return BR_FAILED;
 }
 /*
diff --git a/src/ast/seq_decl_plugin.cpp b/src/ast/seq_decl_plugin.cpp
index 6a0cb3ff8..105a498f9 100644
--- a/src/ast/seq_decl_plugin.cpp
+++ b/src/ast/seq_decl_plugin.cpp
@@ -1093,6 +1093,16 @@ app* seq_util::re::mk_loop(expr* r, unsigned lo, unsigned hi) {
     return m.mk_app(m_fid, OP_RE_LOOP, 2, params, 1, &r);
 }
 
+app* seq_util::re::mk_loop(expr* r, expr* lo) {
+    expr* rs[2] = { r, lo };
+    return m.mk_app(m_fid, OP_RE_LOOP, 0, nullptr, 2, rs);
+}
+
+app* seq_util::re::mk_loop(expr* r, expr* lo, expr* hi) {
+    expr* rs[3] = { r, lo, hi };
+    return m.mk_app(m_fid, OP_RE_LOOP, 0, nullptr, 3, rs);
+}
+
 app* seq_util::re::mk_full_char(sort* s) {
     return m.mk_app(m_fid, OP_RE_FULL_CHAR_SET, 0, nullptr, 0, nullptr, s);
 }
@@ -1129,3 +1139,28 @@ bool seq_util::re::is_loop(expr const* n, expr*& body, unsigned& lo)  {
     }
     return false;
 }
+
+bool seq_util::re::is_loop(expr const* n, expr*& body, expr*& lo, expr*& hi)  {
+    if (is_loop(n)) {
+        app const* a = to_app(n);
+        if (a->get_num_args() == 3) {
+            body = a->get_arg(0);
+            lo = a->get_arg(1);
+            hi = a->get_arg(2);
+            return true;
+        }
+    }
+    return false;
+}
+
+bool seq_util::re::is_loop(expr const* n, expr*& body, expr*& lo)  {
+    if (is_loop(n)) {
+        app const* a = to_app(n);
+        if (a->get_num_args() == 2) {
+            body = a->get_arg(0);
+            lo = a->get_arg(1);
+            return true;
+        }
+    }
+    return false;
+}
diff --git a/src/ast/seq_decl_plugin.h b/src/ast/seq_decl_plugin.h
index 471ed0229..c72252641 100644
--- a/src/ast/seq_decl_plugin.h
+++ b/src/ast/seq_decl_plugin.h
@@ -366,6 +366,8 @@ public:
         app* mk_opt(expr* r) { return m.mk_app(m_fid, OP_RE_OPTION, r); }
         app* mk_loop(expr* r, unsigned lo);
         app* mk_loop(expr* r, unsigned lo, unsigned hi);
+        app* mk_loop(expr* r, expr* lo);
+        app* mk_loop(expr* r, expr* lo, expr* hi);
         app* mk_full_char(sort* s);
         app* mk_full_seq(sort* s);
         app* mk_empty(sort* s);
@@ -394,6 +396,8 @@ public:
         MATCH_UNARY(is_opt);
         bool is_loop(expr const* n, expr*& body, unsigned& lo, unsigned& hi);
         bool is_loop(expr const* n, expr*& body, unsigned& lo);
+        bool is_loop(expr const* n, expr*& body, expr*& lo, expr*& hi);
+        bool is_loop(expr const* n, expr*& body, expr*& lo);
         bool is_unroll(expr const* n) const { return is_app_of(n, m_fid, _OP_RE_UNROLL); }
     };
     str str;