diff --git a/src/stv/mod.rs b/src/stv/mod.rs
index b9c88e6..20698a7 100644
--- a/src/stv/mod.rs
+++ b/src/stv/mod.rs
@@ -224,7 +224,10 @@ impl STVOptions {
 			if self.sample_per_ballot && !self.immediate_elect { return Err(STVError::InvalidOptions("--sample-per-ballot is incompatible with --no-immediate-elect")); }
 			if self.constraints_path.is_some() && self.constraint_mode == ConstraintMode::RepeatCount { return Err(STVError::InvalidOptions("--constraint-mode repeat_count requires a Gregory method for --surplus")); } // TODO: NYI?
 		}
-		if self.subtract_nontransferable && !self.transferable_only { return Err(STVError::InvalidOptions("--subtract-nontransferable requires --transferable-only")) }
+		if self.subtract_nontransferable {
+			if self.surplus != SurplusMethod::WIG { return Err(STVError::InvalidOptions("--subtract-nontransferable requires --surplus wig")) }
+			if !self.transferable_only { return Err(STVError::InvalidOptions("--subtract-nontransferable requires --transferable-only")) }
+		}
 		if self.min_threshold != "0" && self.defer_surpluses { return Err(STVError::InvalidOptions("--min-threshold is incompatible with --defer-surpluses (not yet implemented)")); } // TODO: NYI
 		if self.round_subtransfers == RoundSubtransfersMode::ByValueAndSource && self.bulk_exclude { return Err(STVError::InvalidOptions("--round-subtransfers by_value_and_source is incompatible with --bulk-exclude (not yet implemented)")); } // TODO: NYI
 		return Ok(());