diff --git a/src/ast/rewriter/seq_rewriter.cpp b/src/ast/rewriter/seq_rewriter.cpp
index 0503b73f8..b7871c0e8 100644
--- a/src/ast/rewriter/seq_rewriter.cpp
+++ b/src/ast/rewriter/seq_rewriter.cpp
@@ -1950,7 +1950,7 @@ br_status seq_rewriter::mk_str_lt(expr* a, expr* b, expr_ref& result) {
 br_status seq_rewriter::mk_str_from_code(expr* a, expr_ref& result) {
     rational r;
     if (m_autil.is_numeral(a, r)) {
-        if (r.is_neg() || r > zstring::max_char()) {
+        if (r.is_neg() || r > u().max_char()) {
             result = str().mk_string(symbol(""));
         }
         else {
@@ -3979,19 +3979,19 @@ void seq_rewriter::elim_condition(expr* elem, expr_ref& cond) {
     if (u().is_char(elem)) {
         unsigned ch = 0;
         svector<std::pair<unsigned, unsigned>> ranges, ranges1;
-        ranges.push_back(std::make_pair(0, zstring::max_char()));
+        ranges.push_back(std::make_pair(0, u().max_char()));
         auto exclude_char = [&](unsigned ch) {
             if (ch == 0) {
-                intersect(1, zstring::max_char(), ranges);
+                intersect(1, u().max_char(), ranges);
             }
-            else if (ch == zstring::max_char()) {
+            else if (ch == u().max_char()) {
                 intersect(0, ch-1, ranges);
             }
             else {
                 ranges1.reset();
                 ranges1.append(ranges);
                 intersect(0, ch - 1, ranges);
-                intersect(ch + 1, zstring::max_char(), ranges1);
+                intersect(ch + 1, u().max_char(), ranges1);
                 ranges.append(ranges1);
             }
         };
@@ -4007,7 +4007,7 @@ void seq_rewriter::elim_condition(expr* elem, expr_ref& cond) {
                 intersect(0, ch, ranges);
             }
             else if (u().is_char_le(e, lhs, rhs) && elem == rhs && u().is_const_char(lhs, ch)) {
-                intersect(ch, zstring::max_char(), ranges);
+                intersect(ch, u().max_char(), ranges);
             }
             else if (m().is_not(e, e1) && m().is_eq(e1, lhs, rhs) && elem == lhs && u().is_const_char(rhs, ch)) {
                 exclude_char(ch);
@@ -4017,10 +4017,10 @@ void seq_rewriter::elim_condition(expr* elem, expr_ref& cond) {
             }
             else if (m().is_not(e, e1) && u().is_char_le(e1, lhs, rhs) && elem == lhs && u().is_const_char(rhs, ch)) {
                 // not (e <= ch)
-                if (ch == zstring::max_char()) 
+                if (ch == u().max_char()) 
                     ranges.reset();
                 else 
-                    intersect(ch+1, zstring::max_char(), ranges);
+                    intersect(ch+1, u().max_char(), ranges);
             }
             else if (m().is_not(e, e1) && u().is_char_le(e1, lhs, rhs) && elem == rhs && u().is_const_char(lhs, ch)) {
                 // not (ch <= e)
diff --git a/src/ast/seq_decl_plugin.cpp b/src/ast/seq_decl_plugin.cpp
index ff6d84e4d..a2a0e1da0 100644
--- a/src/ast/seq_decl_plugin.cpp
+++ b/src/ast/seq_decl_plugin.cpp
@@ -180,7 +180,7 @@ bool zstring::uses_unicode() const {
 
 bool zstring::well_formed() const {
     for (unsigned ch : m_buffer) {
-        if (ch > max_char())
+        if (ch > unicode_max_char())
             return false;
     }
     return true;
@@ -398,9 +398,8 @@ seq_decl_plugin::seq_decl_plugin(): m_init(false),
 }
 
 void seq_decl_plugin::finalize() {
-    for (psig* s : m_sigs) {
+    for (psig* s : m_sigs) 
         dealloc(s);
-    }
     m_manager->dec_ref(m_string);
     m_manager->dec_ref(m_char);
     m_manager->dec_ref(m_reglan);
@@ -938,7 +937,7 @@ func_decl * seq_decl_plugin::mk_func_decl(decl_kind k, unsigned num_parameters,
         if (!(num_parameters == 1 && arity == 0 && 
               parameters[0].is_int() && 
               0 <= parameters[0].get_int() && 
-              parameters[0].get_int() < static_cast<int>(zstring::max_char()))) {
+              parameters[0].get_int() < static_cast<int>(max_char()))) {
             m.raise_exception("invalid character declaration");
         }
         return m.mk_const_decl(m_charc_sym, m_char, func_decl_info(m_family_id, OP_CHAR_CONST, num_parameters, parameters));
diff --git a/src/ast/seq_decl_plugin.h b/src/ast/seq_decl_plugin.h
index 5b9fc5114..39fbb1fc6 100644
--- a/src/ast/seq_decl_plugin.h
+++ b/src/ast/seq_decl_plugin.h
@@ -118,8 +118,10 @@ private:
     bool uses_unicode() const;
     bool is_escape_char(char const *& s, unsigned& result);
 public:
-    static unsigned max_char() { return 196607; }
-    static unsigned num_bits() { return 16; }
+    static unsigned unicode_max_char() { return 196607; }
+    static unsigned unicode_num_bits() { return 18; }
+    static unsigned ascii_max_char() { return 255; }
+    static unsigned ascii_num_bits() { return 8; }
     zstring() {}
     zstring(char const* s);
     zstring(const std::string &str) : zstring(str.c_str()) {}
@@ -225,6 +227,9 @@ public:
 
     bool is_char(ast* a) const { return a == m_char; }
 
+    unsigned max_char() const { return m_unicode ? zstring::unicode_max_char() : zstring::ascii_max_char(); }
+    unsigned num_bits() const { return m_unicode ? zstring::unicode_num_bits() : zstring::ascii_num_bits(); }
+
     app* mk_string(symbol const& s);
     app* mk_string(zstring const& s);
     app* mk_char(unsigned ch);
@@ -266,6 +271,8 @@ public:
     app* mk_char(unsigned ch) const;
     app* mk_le(expr* ch1, expr* ch2) const;
     app* mk_lt(expr* ch1, expr* ch2) const;    
+    unsigned max_char() const { return seq.max_char(); }
+    unsigned num_bits() const { return seq.num_bits(); }
 
     app* mk_skolem(symbol const& name, unsigned n, expr* const* args, sort* range);
     bool is_skolem(expr const* e) const { return is_app_of(e, m_fid, _OP_SEQ_SKOLEM); }
diff --git a/src/smt/seq_axioms.cpp b/src/smt/seq_axioms.cpp
index 4f48f20f2..0ca0a5500 100644
--- a/src/smt/seq_axioms.cpp
+++ b/src/smt/seq_axioms.cpp
@@ -811,7 +811,7 @@ void seq_axioms::add_str_to_code_axiom(expr* n) {
     VERIFY(seq.str.is_to_code(n, e)); 
     literal len_is1 = mk_eq(mk_len(e), a.mk_int(1));
     add_axiom(~len_is1, mk_ge(n, 0)); 
-    add_axiom(~len_is1, mk_le(n, zstring::max_char()));
+    add_axiom(~len_is1, mk_le(n, seq.max_char()));
     add_axiom(len_is1, mk_eq(n, a.mk_int(-1)));
 }
 
@@ -824,7 +824,7 @@ void seq_axioms::add_str_from_code_axiom(expr* n) {
     expr* e = nullptr;
     VERIFY(seq.str.is_from_code(n, e)); 
     literal ge = mk_ge(e, 0);
-    literal le = mk_le(e, zstring::max_char());
+    literal le = mk_le(e, seq.max_char());
     literal emp = mk_literal(seq.str.mk_is_empty(n));
     add_axiom(~ge, ~le, mk_eq(mk_len(n), a.mk_int(1)));
     add_axiom(~ge, ~le, mk_eq(seq.str.mk_to_code(n), e));
diff --git a/src/smt/seq_unicode.cpp b/src/smt/seq_unicode.cpp
index 4a4de8412..65ec93277 100644
--- a/src/smt/seq_unicode.cpp
+++ b/src/smt/seq_unicode.cpp
@@ -81,7 +81,7 @@ namespace smt {
             }            
         }
         else {            
-            for (unsigned i = 0; i < zstring::num_bits(); ++i) 
+            for (unsigned i = 0; i < seq.num_bits(); ++i) 
                 ebits.push_back(seq.mk_char_bit(e, i));
             ctx().internalize(ebits.c_ptr(), ebits.size(), true);
             for (expr* arg : ebits)
@@ -92,7 +92,9 @@ namespace smt {
             ctx().mark_as_relevant(bits2char);
             enode* n1 = th.ensure_enode(e);
             enode* n2 = th.ensure_enode(bits2char);
-            justification* j = ctx().mk_justification(ext_theory_eq_propagation_justification(th.get_id(), ctx().get_region(), 0, nullptr, 0, nullptr, n1, n2));
+            justification* j = 
+                ctx().mk_justification(
+                    ext_theory_eq_propagation_justification(th.get_id(), ctx().get_region(), n1, n2));
             ctx().assign_eq(n1, n2, eq_justification(j));
         }
         ++m_stats.m_num_blast;
@@ -206,7 +208,7 @@ namespace smt {
                     enforce_ackerman(u, v);
                     return false;
                 }
-                if (c >= zstring::max_char()) {
+                if (c >= seq.max_char()) {
                     enforce_value_bound(v);
                     return false;
                 }
@@ -232,7 +234,7 @@ namespace smt {
             if (seq.is_char(e) && m_var2value[v] == UINT_MAX) {
                 d = c;
                 while (values.contains(c)) {
-                    c = (c + 1) % zstring::max_char();
+                    c = (c + 1) % seq.max_char();
                     if (d == c) {
                         enforce_bits();
                         return false;
@@ -260,7 +262,7 @@ namespace smt {
 
     void seq_unicode::enforce_value_bound(theory_var v) {
         TRACE("seq", tout << "enforce bound " << v << "\n";);
-        enode* n = th.ensure_enode(seq.mk_char(zstring::max_char()));
+        enode* n = th.ensure_enode(seq.mk_char(seq.max_char()));
         theory_var w = n->get_th_var(th.get_id());                    
         SASSERT(has_bits(w));
         init_bits(v);
@@ -317,7 +319,7 @@ namespace smt {
     void seq_unicode::collect_statistics(::statistics& st) const {
         st.update("seq char ackerman", m_stats.m_num_ackerman);
         st.update("seq char bounds",   m_stats.m_num_bounds);
-        st.update("seq char2bit",    m_stats.m_num_blast);
+        st.update("seq char2bit",      m_stats.m_num_blast);
     }
 }
 
diff --git a/src/smt/smt_justification.h b/src/smt/smt_justification.h
index 848cf26e9..48987e746 100644
--- a/src/smt/smt_justification.h
+++ b/src/smt/smt_justification.h
@@ -373,6 +373,12 @@ namespace smt {
             unsigned num_params = 0, parameter* params = nullptr):
             ext_theory_simple_justification(fid, r, num_lits, lits, num_eqs, eqs, num_params, params), m_lhs(lhs), m_rhs(rhs) {}
 
+        ext_theory_eq_propagation_justification(
+            family_id fid, region & r, 
+            enode * lhs, enode * rhs):
+            ext_theory_simple_justification(fid, r, 0, nullptr, 0, nullptr, 0, nullptr), m_lhs(lhs), m_rhs(rhs) {}
+
+        
         proof * mk_proof(conflict_resolution & cr) override;
 
         char const * get_name() const override { return "ext-theory-eq-propagation"; }