diff --git a/gtsam/inference/Factor-inl.h b/gtsam/inference/Factor-inl.h
index d05cc1de3..d9fb1e0de 100644
--- a/gtsam/inference/Factor-inl.h
+++ b/gtsam/inference/Factor-inl.h
@@ -45,12 +45,12 @@ namespace gtsam {
 	void Factor<KEY>::assertInvariants() const {
 #ifndef NDEBUG
 		// Check that keys are all unique
-		std::multiset < KeyType > nonunique(keys_.begin(), keys_.end());
-		std::set < KeyType > unique(keys_.begin(), keys_.end());
+		std::multiset<KeyType> nonunique(keys_.begin(), keys_.end());
+		std::set<KeyType> unique(keys_.begin(), keys_.end());
 		bool correct = (nonunique.size() == unique.size())
 				&& std::equal(nonunique.begin(), nonunique.end(), unique.begin());
 		if (!correct) throw std::logic_error(
-				"Factor::assertInvariants: detected inconsistency");
+				"Factor::assertInvariants: Factor contains duplicate keys");
 #endif
 	}