See https://groups.google.com/forum/#!topic/minisat/FCocZsC8oMQ This seems to only be a problem with newer versions of g++, and upstream development seems to have stopped in 2013. diff -rupN minisat-2.2.0/core/SolverTypes.h minisat-2.2.0.patched/core/SolverTypes.h --- a/minisat/core/SolverTypes.h 2010-07-10 17:07:36.000000000 +0100 +++ b/minisat/core/SolverTypes.h 2014-03-29 11:57:49.000000000 +0000 @@ -47,7 +47,7 @@ struct Lit { int x; // Use this as a constructor: - friend Lit mkLit(Var var, bool sign = false); + //friend Lit mkLit(Var var, bool sign = false); bool operator == (Lit p) const { return x == p.x; } bool operator != (Lit p) const { return x != p.x; } @@ -55,7 +55,7 @@ struct Lit { }; -inline Lit mkLit (Var var, bool sign) { Lit p; p.x = var + var + (int)sign; return p; } +inline Lit mkLit (Var var, bool sign = false) { Lit p; p.x = var + var + (int)sign; return p; } inline Lit operator ~(Lit p) { Lit q; q.x = p.x ^ 1; return q; } inline Lit operator ^(Lit p, bool b) { Lit q; q.x = p.x ^ (unsigned int)b; return q; } inline bool sign (Lit p) { return p.x & 1; }