diff --git a/frontend/components/token-classifier/results/TextSpan.vue b/frontend/components/token-classifier/results/TextSpan.vue
index 809e5d7067..f512a4daa1 100755
--- a/frontend/components/token-classifier/results/TextSpan.vue
+++ b/frontend/components/token-classifier/results/TextSpan.vue
@@ -76,6 +76,7 @@
 import ClickOutside from "v-click-outside";
 import "assets/icons/check";
 import "assets/icons/cross";
+import { substring } from "stringz";
 
 export default {
   directives: {
@@ -113,13 +114,15 @@ export default {
       return this.spans[this.spanId];
     },
     text() {
-      return this.record.raw_text.slice(
+      return substring(
+        this.record.raw_text,
         this.spans[this.spanId].start,
         this.spans[this.spanId].end
       );
     },
     whiteSpace() {
-      return this.record.raw_text.slice(
+      return substring(
+        this.record.raw_text,
         this.spans[this.spanId].end,
         this.spans[this.spanId + 1] ? this.spans[this.spanId + 1].start : ""
       );
diff --git a/frontend/models/TokenClassification.js b/frontend/models/TokenClassification.js
index ac25286318..2473095fbc 100644
--- a/frontend/models/TokenClassification.js
+++ b/frontend/models/TokenClassification.js
@@ -17,6 +17,7 @@
 
 import { ObservationDataset, USER_DATA_METADATA_KEY } from "./Dataset";
 import { BaseRecord, BaseSearchQuery, BaseSearchResults } from "./Common";
+import { indexOf, length } from "stringz";
 
 class TokenClassificationRecord extends BaseRecord {
   tokens;
@@ -28,8 +29,8 @@ class TokenClassificationRecord extends BaseRecord {
     super({ ...superData });
     const { visualTokens } = tokens.reduce(
       ({ visualTokens, startPosition }, token) => {
-        const start = raw_text.indexOf(token, startPosition);
-        const end = start + token.length;
+        const start = indexOf(raw_text, token, startPosition);
+        const end = start + length(token);
         return {
           visualTokens: [...visualTokens, { start, end, text: token }],
           startPosition: end,
diff --git a/frontend/package.json b/frontend/package.json
index 2d16b3dcd2..06b792d6c4 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -33,6 +33,7 @@
     "nuxt": "^2.14.6",
     "nuxt-highlightjs": "^1.0.1",
     "sass-loader": "^10.1.0",
+    "stringz": "^2.1.0",
     "v-click-outside": "^3.1.2",
     "vue-moment": "^4.1.0",
     "vue-svgicon": "^3.2.9",
@@ -59,4 +60,4 @@
     "prettier": "^2.2.1",
     "vue-jest": "^3.0.7"
   }
-}
\ No newline at end of file
+}