diff --git a/lib/assign.test.js b/lib/assign.test.js
index 2b61ea9..fd5ad16 100644
--- a/lib/assign.test.js
+++ b/lib/assign.test.js
@@ -114,6 +114,14 @@ describe("JsonPointer.assign", () => {
         expect(subject[0]).to.equal("foo");
       });
     });
+
+    When("indexing into the array with an invalid index", () => {
+      const assign = JsonPointer.assign("/01");
+
+      Then("an error should be thrown", () => {
+        expect(() => assign(subject, "foo")).to.throw(TypeError, "Value at '' is an array and '01' is not a valid array index");
+      });
+    });
   });
 
   Given("a number", () => {
diff --git a/lib/get.test.js b/lib/get.test.js
index dc9a48d..6b635a6 100644
--- a/lib/get.test.js
+++ b/lib/get.test.js
@@ -49,6 +49,7 @@ describe("JsonPointer", () => {
       ["/bbb/-", { ccc: 13 }],
       ["/bar", undefined],
       ["/foo/2", undefined],
+      ["/foo/01", undefined],
       ["/foo/-", undefined],
       ["/0", undefined]
     ];
diff --git a/lib/index.js b/lib/index.js
index fc1a5cb..98f35df 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -164,7 +164,7 @@ const _set = (segments, index, subject, value) => {
 
   // currentSubject could also be an array, but this appeases the type system
   const currentSubject = /** @type API.JsonObject */ (subject);
-  const computedSegment = computeSegment(subject, segment);
+  const computedSegment = computeSegment(subject, segment, cursorAt(segments, index));
   currentSubject[computedSegment] = _set(segments, index + 1, currentSubject[computedSegment], value);
   return currentSubject;
 };
@@ -210,7 +210,7 @@ const _assign = (segments, subject, value, cursor = nil) => {
   let lastSubject;
 
   for (let segment of segments) {
-    segment = computeSegment(currentSubject, segment);
+    segment = computeSegment(currentSubject, segment, cursor);
     lastSegment = segment;
     lastSubject = currentSubject;
     currentSubject = applySegment(currentSubject, segment, cursor);
@@ -274,13 +274,12 @@ const _unset = (segments, index, subject) => {
 
   // currentSubject could also be an array, but this appeases the type system
   const currentSubject = /** @type API.JsonObject */ (subject);
-  const computedSegment = computeSegment(currentSubject, segment);
-  const unsetSubject = _unset(segments, index + 1, currentSubject[computedSegment]);
-  if (computedSegment in currentSubject) {
+  const unsetSubject = _unset(segments, index + 1, getSegment(currentSubject, segment));
+  if (hasSegment(currentSubject, segment)) {
     if (unsetSubject === undefined) {
-      delete currentSubject[computedSegment];
+      delete currentSubject[segment];
     } else {
-      currentSubject[computedSegment] = unsetSubject;
+      currentSubject[segment] = unsetSubject;
     }
   }
   return currentSubject;
@@ -324,8 +323,7 @@ const _remove = (segments, subject, cursor = nil) => {
   /** @type API.Json | undefined */
   let lastSubject;
 
-  for (let segment of segments) {
-    segment = computeSegment(currentSubject, segment);
+  for (const segment of segments) {
     lastSegment = segment;
     lastSubject = currentSubject;
     currentSubject = applySegment(currentSubject, segment, cursor);
@@ -337,7 +335,10 @@ const _remove = (segments, subject, cursor = nil) => {
   }
 
   // lastSubject could also be an array, but this appeases the type system
-  delete /** @type API.JsonObject */ (lastSubject)[lastSegment];
+  const container = /** @type API.JsonObject */ (lastSubject);
+  if (hasSegment(container, lastSegment)) {
+    delete container[lastSegment];
+  }
 };
 
 /** @type API.append */
@@ -364,23 +365,34 @@ const unescape = (segment) => {
  * @overload
  * @param {API.Json[]} value
  * @param {string} segment
+ * @param {string} cursor
  * @returns {number}
  *
  * @overload
  * @param {API.Json | undefined} value
  * @param {string} segment
+ * @param {string} cursor
  * @returns {string}
  *
  * @param {API.Json | undefined} value
  * @param {string} segment
+ * @param {string} cursor
  * @returns {string | number}
  */
-const computeSegment = (value, segment) => {
-  if (Array.isArray(value)) {
-    return segment === "-" ? value.length : parseInt(segment, 10);
-  } else {
+const computeSegment = (value, segment, cursor) => {
+  if (!Array.isArray(value)) {
     return segment;
   }
+
+  if (segment === "-") {
+    return value.length;
+  }
+
+  if (!/^(?:0|[1-9][0-9]*)$/.test(segment)) {
+    throw TypeError(`Value at '${cursor}' is an array and '${segment}' is not a valid array index`);
+  }
+
+  return Number(segment);
 };
 
 /** @type (value: API.Json | undefined, segment: string, cursor?: string) => API.Json | undefined */
@@ -394,13 +406,15 @@ const applySegment = (value, segment, cursor = "") => {
 
 /** @type (value: API.JsonObject | API.Json[], segment: string) => API.Json | undefined */
 const getSegment = (value, segment) => {
-  const computedSegment = computeSegment(value, segment);
-  if (Object.hasOwn(value, computedSegment)) {
+  if (hasSegment(value, segment)) {
     // value could also be an array, but this appeases the type system
-    return /** @type API.JsonObject */ (value)[computedSegment];
+    return /** @type API.JsonObject */ (value)[segment];
   }
 };
 
+/** @type (value: API.JsonObject | API.Json[], segment: string) => boolean */
+const hasSegment = (value, segment) => Object.prototype.propertyIsEnumerable.call(value, segment);
+
 /** @type (value: API.Json | undefined) => value is API.JsonObject | API.Json[] */
 const isContainer = (value) => typeof value === "object" && value !== null;
 
diff --git a/lib/set.test.js b/lib/set.test.js
index 4bcf9be..c495ade 100644
--- a/lib/set.test.js
+++ b/lib/set.test.js
@@ -192,6 +192,14 @@ describe("JsonPointer.set", () => {
         expect(subject.length).to.equal(0);
       });
     });
+
+    When("indexing into the array with an invalid index", () => {
+      const set = JsonPointer.set("/01");
+
+      Then("an error should be thrown", () => {
+        expect(() => set(subject, "foo")).to.throw(TypeError, "Value at '' is an array and '01' is not a valid array index");
+      });
+    });
   });
 
   Given("a number", () => {