diff --git a/src/smt/params/smt_params_helper.pyg b/src/smt/params/smt_params_helper.pyg
index d6ca8c9b2..937aa6a2b 100644
--- a/src/smt/params/smt_params_helper.pyg
+++ b/src/smt/params/smt_params_helper.pyg
@@ -74,7 +74,7 @@ def_module_params(module_name='smt',
                           ('str.fast_length_tester_cache', BOOL, False, 'cache length tester constants instead of regenerating them'),
                           ('str.fast_value_tester_cache', BOOL, True, 'cache value tester constants instead of regenerating them'),
                           ('str.string_constant_cache', BOOL, True, 'cache all generated string constants generated from anywhere in theory_str'),
-                          ('str.use_binary_search', BOOL, False, 'use a binary search heuristic for finding concrete length values for free variables in theory_str (set to False to use linear search)'),
+                          ('str.use_binary_search', BOOL, True, 'use a binary search heuristic for finding concrete length values for free variables in theory_str (set to False to use linear search)'),
                           ('str.binary_search_start', UINT, 64, 'initial upper bound for theory_str binary search'),
                           ('theory_aware_branching', BOOL, False, 'Allow the context to use extra information from theory solvers regarding literal branching prioritization.'),
                           ('str.finite_overlap_models', BOOL, False, 'attempt a finite model search for overlapping variables instead of completely giving up on the arrangement'),
diff --git a/src/smt/theory_str.cpp b/src/smt/theory_str.cpp
index fc8122800..fb191626f 100644
--- a/src/smt/theory_str.cpp
+++ b/src/smt/theory_str.cpp
@@ -9907,6 +9907,21 @@ namespace smt {
         expr_ref freeVarLen(mk_strlen(freeVar), m);
         SASSERT(freeVarLen);
 
+        {
+            rational freeVar_len_value;
+            if (get_len_value(freeVar, freeVar_len_value)) {
+                TRACE("str", tout << "special case: length of freeVar is known to be " << freeVar_len_value << std::endl;);
+                expr_ref concreteOption(ctx.mk_eq_atom(indicator, mk_string(freeVar_len_value.to_string().c_str()) ), m);
+                expr_ref concreteValue(ctx.mk_eq_atom(
+                        ctx.mk_eq_atom(indicator, mk_string(freeVar_len_value.to_string().c_str()) ),
+                        ctx.mk_eq_atom(freeVarLen, m_autil.mk_numeral(freeVar_len_value, true))), m);
+                expr_ref finalAxiom(m.mk_and(concreteOption, concreteValue), m);
+                SASSERT(finalAxiom);
+                m_trail.push_back(finalAxiom);
+                return finalAxiom;
+            }
+        }
+
         expr_ref_vector orList(m);
         expr_ref_vector andList(m);
 
@@ -10221,6 +10236,16 @@ namespace smt {
             }
             refresh_theory_var(firstTester);
 
+            {
+                rational freeVar_len_value;
+                if (get_len_value(freeVar, freeVar_len_value)) {
+                    TRACE("str", tout << "special case: length of freeVar is known to be " << freeVar_len_value << std::endl;);
+                    midPoint = freeVar_len_value;
+                    upperBound = midPoint * 2;
+                    windowSize = upperBound;
+                }
+            }
+
             binary_search_len_tester_stack[freeVar].push_back(firstTester);
             m_trail_stack.push(binary_search_trail<theory_str>(binary_search_len_tester_stack, freeVar));
             binary_search_info new_info(lowerBound, midPoint, upperBound, windowSize);