diff --git a/src/sat/bsat/satVec.h b/src/sat/bsat/satVec.h
index 8cc8ba4eb5..305df9160c 100644
--- a/src/sat/bsat/satVec.h
+++ b/src/sat/bsat/satVec.h
@@ -130,7 +130,9 @@ static inline void   vecp_remove(vecp* v, void* e)
 typedef int    lit;
 typedef int    cla;
 
-typedef char               lbool;
+// Explicitly make it signed so promotion-to-int behavior doesn't vary
+// across platforms that define signedness of char differently.
+typedef signed char lbool;
 
 static const int   var_Undef = -1;
 static const lit   lit_Undef = -2;