diff --git a/greg/nfa.go b/greg/nfa.go
index a3dd632..9b3811f 100644
--- a/greg/nfa.go
+++ b/greg/nfa.go
@@ -150,12 +150,12 @@ func (s State) checkAssertion(str []rune, idx int) bool {
 		numMatchesFound := 0
 		for _, matchIdx := range matchIndices {
 			if s.assert == PLA || s.assert == NLA { // Lookahead - return true (or false) if at least one match starts at 0. Zero is used because the test-string _starts_ from idx.
-				if matchIdx[0].startIdx == 0 {
+				if matchIdx[0].StartIdx == 0 {
 					numMatchesFound++
 				}
 			}
 			if s.assert == PLB || s.assert == NLB { // Lookbehind - return true (or false) if at least one match _ends_ at the current index.
-				if matchIdx[0].endIdx == idx {
+				if matchIdx[0].EndIdx == idx {
 					numMatchesFound++
 				}
 			}