diff --git a/matching.go b/matching.go
index 11ddaf3..e32ff6e 100644
--- a/matching.go
+++ b/matching.go
@@ -97,7 +97,7 @@ func findAllMatchesHelper(start *State, str string, indices []matchIndex, offset
 
 	// Increment until we hit a character matching the start state (assuming not 0-state)
 	if start.isEmpty == false {
-		for i < len(str) && !start.contentContains([]rune(str), i) {
+		for i < len(str) && !start.contentContains(str, i) {
 			i++
 		}
 		startIdx = i
@@ -136,7 +136,7 @@ func findAllMatchesHelper(start *State, str string, indices []matchIndex, offset
 		numStatesMatched := 0    // The number of states which had at least 1 match for this round
 		assertionFailed := false // Whether or not an assertion failed for this round
 		for _, state := range currentStates {
-			matches, numMatches := state.matchesFor([]rune(str), i)
+			matches, numMatches := state.matchesFor(str, i)
 			if numMatches > 0 {
 				numStatesMatched++
 				tempStates = append(tempStates, matches...)
@@ -211,7 +211,7 @@ func findAllMatchesHelper(start *State, str string, indices []matchIndex, offset
 		// Only add the match if the start index is in bounds. If the state has an assertion,
 		// make sure the assertion checks out.
 		if state.isLast && startIdx < len(str) {
-			if state.assert == NONE || state.checkAssertion([]rune(str), len(str)) {
+			if state.assert == NONE || state.checkAssertion(str, len(str)) {
 				endIdx = i
 				tempIndices, _ = unique_append(tempIndices, matchIndex{startIdx, endIdx})
 			}
diff --git a/misc.go b/misc.go
index f8a6953..bf6304e 100644
--- a/misc.go
+++ b/misc.go
@@ -22,11 +22,12 @@ func dotChars() []rune { // Returns all possible characters represented by the d
 }
 
 // Returns true if str[idx] and str[idx-1] are separated by a word boundary.
-func isWordBoundary(str []rune, idx int) bool {
+func isWordBoundary(str string, idx int) bool {
+	str_runes := []rune(str)
 	wbounded := idx == 0 ||
 		idx >= len(str)-1 ||
-		(!slices.Contains(wordChars, str[idx-1]) && slices.Contains(wordChars, str[idx])) ||
-		(slices.Contains(wordChars, str[idx-1]) && !slices.Contains(wordChars, str[idx]))
+		(!slices.Contains(wordChars, str_runes[idx-1]) && slices.Contains(wordChars, str_runes[idx])) ||
+		(slices.Contains(wordChars, str_runes[idx-1]) && !slices.Contains(wordChars, str_runes[idx]))
 	return wbounded
 }
 
diff --git a/nfa.go b/nfa.go
index 3457fd9..65b30fc 100644
--- a/nfa.go
+++ b/nfa.go
@@ -27,7 +27,7 @@ type State struct {
 
 // Checks if the given state's assertion is true. Returns true if the given
 // state doesn't have an assertion.
-func (s State) checkAssertion(str []rune, idx int) bool {
+func (s State) checkAssertion(str string, idx int) bool {
 	if s.assert == SOS {
 		return idx == 0
 	}
@@ -44,7 +44,7 @@ func (s State) checkAssertion(str []rune, idx int) bool {
 }
 
 // Returns true if the contents of 's' contain the value at the given index of the given string
-func (s State) contentContains(str []rune, idx int) bool {
+func (s State) contentContains(str string, idx int) bool {
 	if s.assert != NONE {
 		return s.checkAssertion(str, idx)
 	}
@@ -54,7 +54,7 @@ func (s State) contentContains(str []rune, idx int) bool {
 
 // Returns the matches for the character at the given index of the given string.
 // Also returns the number of matches. Returns -1 if an assertion failed.
-func (s State) matchesFor(str []rune, idx int) ([]*State, int) {
+func (s State) matchesFor(str string, idx int) ([]*State, int) {
 	// Assertions can be viewed as 'checks'. If the check fails, we return
 	// an empty array and 0.
 	// If it passes, we treat it like any other state, and return all the transitions.