diff --git a/src/ast/rewriter/seq_rewriter.cpp b/src/ast/rewriter/seq_rewriter.cpp
index 2406e92ed..857cc0e36 100644
--- a/src/ast/rewriter/seq_rewriter.cpp
+++ b/src/ast/rewriter/seq_rewriter.cpp
@@ -689,11 +689,10 @@ br_status seq_rewriter::mk_seq_extract(expr* a, expr* b, expr* c, expr_ref& resu
     if (offset == 0) {
         return BR_FAILED;
     }
-    expr_ref len1(m()), pos1(m());
+    expr_ref pos1(m());
     pos1 = m_autil.mk_sub(b, m_autil.mk_int(offset));
-    len1 = m_autil.mk_sub(c, m_autil.mk_int(offset));
     result = m_util.str.mk_concat(as.size() - offset, as.c_ptr() + offset);
-    result = m_util.str.mk_substr(result, pos1, len1);
+    result = m_util.str.mk_substr(result, pos1, c);
     return BR_REWRITE3;
 }
 
diff --git a/src/smt/theory_seq.cpp b/src/smt/theory_seq.cpp
index 9be03ad6e..d9bb352aa 100644
--- a/src/smt/theory_seq.cpp
+++ b/src/smt/theory_seq.cpp
@@ -4735,7 +4735,6 @@ bool theory_seq::get_length(expr* e, rational& val) const {
 }
 
 /*
-  TBD: check semantics of extract.
 
   let e = extract(s, i, l)
 
@@ -4797,15 +4796,16 @@ void theory_seq::add_extract_axiom(expr* e) {
     literal li_ge_ls  = mk_simplified_literal(m_autil.mk_ge(ls_minus_i_l, zero));
     literal l_ge_zero = mk_simplified_literal(m_autil.mk_ge(l, zero));
     literal ls_le_0   = mk_simplified_literal(m_autil.mk_le(ls, zero));
+    literal le_is_0   = mk_eq(le, zero, false);
 
     add_axiom(~i_ge_0, ~ls_le_i, mk_seq_eq(xey, s));
     add_axiom(~i_ge_0, ~ls_le_i, mk_eq(lx, i, false));
     add_axiom(~i_ge_0, ~ls_le_i, ~l_ge_zero, ~li_ge_ls, mk_eq(le, l, false));
     add_axiom(~i_ge_0, ~ls_le_i, li_ge_ls, mk_eq(le, mk_sub(ls, i), false));
     add_axiom(~i_ge_0, ~ls_le_i, l_ge_zero, mk_eq(le, zero, false));
-    add_axiom(i_ge_0, mk_eq(le, zero, false));
-    add_axiom(ls_le_i, mk_eq(le, zero, false));
-    add_axiom(~ls_le_0, mk_eq(le, zero, false));
+    add_axiom(i_ge_0,   le_is_0);
+    add_axiom(ls_le_i,  le_is_0);
+    add_axiom(~ls_le_0, le_is_0);
 }
 
 void theory_seq::add_tail_axiom(expr* e, expr* s) {