diff --git a/lib/construct.c b/lib/construct.c
index e54bcc6..62bf32d 100644
--- a/lib/construct.c
+++ b/lib/construct.c
@@ -33,6 +33,8 @@ static void construct_term(const regex_term_t *term, fsa_t *out)
 	case REGEX_TERM_CLASS:
 		assert(false);
 	}
+
+	assert(out->states[0].final);
 }
 
 static void concat_fsas(fsa_t *base, const fsa_t *other)
@@ -65,6 +67,8 @@ static void concat_fsas(fsa_t *base, const fsa_t *other)
 
 	free(other->states[0].rules);
 	free(other->states);
+
+	assert(base->states[0].final);
 }
 
 static void construct_sequence(const regex_sequence_t *seq, fsa_t *out)
@@ -77,6 +81,8 @@ static void construct_sequence(const regex_sequence_t *seq, fsa_t *out)
 		construct_term(&seq->contents[i], &term_fsa);
 		concat_fsas(out, &term_fsa);
 	}
+
+	assert(out->states[0].final);
 }
 
 void construct(const regex_t *regex, fsa_t *out)