diff --git a/src/smt/smt_parallel.cpp b/src/smt/smt_parallel.cpp
index 0b5afcae5..6a0a18bd5 100644
--- a/src/smt/smt_parallel.cpp
+++ b/src/smt/smt_parallel.cpp
@@ -15,12 +15,24 @@ Author:
 
 --*/
 
+
 #include "util/scoped_ptr_vector.h"
 #include "ast/ast_util.h"
 #include "ast/ast_pp.h"
 #include "ast/ast_translation.h"
 #include "smt/smt_parallel.h"
 #include "smt/smt_lookahead.h"
+
+#ifdef SINGLE_THREAD
+
+namespace smt {
+    
+    lbool parallel::operator()(expr_ref_vector const& asms) {
+        return l_undef;
+    }
+
+#else
+
 #include <thread>
 
 namespace smt {
@@ -234,3 +246,4 @@ namespace smt {
     }
 
 }
+#endif
diff --git a/src/solver/parallel_tactic.cpp b/src/solver/parallel_tactic.cpp
index 564788194..1cb71e99b 100644
--- a/src/solver/parallel_tactic.cpp
+++ b/src/solver/parallel_tactic.cpp
@@ -28,6 +28,17 @@ Notes:
  
 --*/
 
+#include "util/scoped_ptr_vector.h"
+#include "ast/ast_pp.h"
+#include "ast/ast_util.h"
+#include "ast/ast_translation.h"
+#include "solver/solver.h"
+#include "solver/solver2tactic.h"
+#include "tactic/tactic.h"
+#include "tactic/tactical.h"
+#include "solver/parallel_tactic.h"
+#include "solver/parallel_params.hpp"
+
 #ifdef SINGLE_THREAD
 
 tactic * mk_parallel_tactic(solver* s, params_ref const& p) {
@@ -40,16 +51,6 @@ tactic * mk_parallel_tactic(solver* s, params_ref const& p) {
 #include <mutex>
 #include <cmath>
 #include <condition_variable>
-#include "util/scoped_ptr_vector.h"
-#include "ast/ast_pp.h"
-#include "ast/ast_util.h"
-#include "ast/ast_translation.h"
-#include "solver/solver.h"
-#include "solver/solver2tactic.h"
-#include "tactic/tactic.h"
-#include "tactic/tactical.h"
-#include "solver/parallel_tactic.h"
-#include "solver/parallel_params.hpp"
 
 class parallel_tactic : public tactic {