diff --git a/__TEST__/hyperaudio-lite.test.js b/__TEST__/hyperaudio-lite.test.js
index 5b9ff0d..5633920 100644
--- a/__TEST__/hyperaudio-lite.test.js
+++ b/__TEST__/hyperaudio-lite.test.js
@@ -158,6 +158,22 @@ test("createWordArray", () => {
   expect(ht.createWordArray(words)).toStrictEqual(expectedResult);
 });
 
+test("createWordArray ignores malformed data-m values", () => {
+  const container = document.createElement("p");
+  container.innerHTML =
+    '<span data-m="100">valid</span>' +
+    '<span class="read active" data-m="">invalid</span>' +
+    '<span data-m="300">valid</span>';
+
+  const result = ht.createWordArray(container.querySelectorAll("[data-m]"));
+  const invalidWord = container.children[1];
+
+  expect(result.map(({ m }) => m)).toEqual([100, 300]);
+  expect(invalidWord.classList.contains("unread")).toBe(true);
+  expect(invalidWord.classList.contains("read")).toBe(false);
+  expect(invalidWord.classList.contains("active")).toBe(false);
+});
+
 test("getSelectionMediaFragment", () => {
   document
     .getSelection()
@@ -414,6 +430,25 @@ test("setPlayHead updates currentTime and plays if playOnClick is true", () => {
   expect(ht.myPlayer.play).toHaveBeenCalled();
 });
 
+test("setPlayHead ignores targets without a numeric data-m", () => {
+  ht.playOnClick = true;
+  ht.highlightedText = true;
+  ht.myPlayer = { setTime: jest.fn(), play: jest.fn(), paused: true };
+  const updateSpy = jest.spyOn(ht, "updateTranscriptVisualState");
+  const activeWord = document.querySelector('span[data-m="3950"]');
+  activeWord.classList.add("active");
+
+  ht.setPlayHead({ target: activeWord.parentNode });
+
+  expect(updateSpy).not.toHaveBeenCalled();
+  expect(ht.myPlayer.setTime).not.toHaveBeenCalled();
+  expect(ht.myPlayer.play).not.toHaveBeenCalled();
+  expect(ht.highlightedText).toBe(true);
+  expect(activeWord.classList.contains("active")).toBe(true);
+
+  updateSpy.mockRestore();
+});
+
 test("preparePlayHead sets paused to false and calls checkPlayHead", () => {
   ht.checkPlayHead = jest.fn();
   ht.preparePlayHead();
diff --git a/js/hyperaudio-lite.js b/js/hyperaudio-lite.js
index c86b2a3..fcc3a8d 100644
--- a/js/hyperaudio-lite.js
+++ b/js/hyperaudio-lite.js
@@ -631,8 +631,23 @@ class HyperaudioLite {
 
   // Create an array of words with metadata from the transcript
   createWordArray(words) {
-    return Array.from(words).map(word => {
+    const wordArr = [];
+
+    Array.from(words).forEach(word => {
       const m = parseInt(word.getAttribute('data-m'));
+
+      // Reset to a clean baseline — stale read/active classes from a previous
+      // instance on the same DOM would survive the delta updates in
+      // updateTranscriptVisualState (#251).
+      word.classList.remove('read', 'active');
+      word.classList.add('unread');
+
+      // A malformed timestamp breaks every binary-search comparison that
+      // probes it. Keep the DOM node inert instead of poisoning playback.
+      if (Number.isNaN(m)) {
+        return;
+      }
+
       let p = word.parentNode;
       while (p !== document) {
         if (['p', 'figure', 'ul'].includes(p.tagName.toLowerCase())) {
@@ -640,13 +655,11 @@ class HyperaudioLite {
         }
         p = p.parentNode;
       }
-      // Reset to a clean baseline — stale read/active classes from a previous
-      // instance on the same DOM would survive the delta updates in
-      // updateTranscriptVisualState (#251).
-      word.classList.remove('read', 'active');
-      word.classList.add('unread');
-      return { n: word, m, p };
+
+      wordArr.push({ n: word, m, p });
     });
+
+    return wordArr;
   }
 
   getSelectionRange = () => {
@@ -721,10 +734,19 @@ class HyperaudioLite {
     }
 
     const target = e.target || e.srcElement;
+    const timeSecs = target && target.dataset
+      ? parseInt(target.dataset.m) / 1000
+      : NaN;
+
+    // Clicks on transcript whitespace or malformed timed nodes must not update
+    // the visual-state binary search with NaN.
+    if (Number.isNaN(timeSecs)) {
+      return;
+    }
+
     this.highlightedText = false;
     this.clearActiveClasses();
 
-    const timeSecs = parseInt(target.dataset.m) / 1000;
     this.updateTranscriptVisualState(timeSecs);
 
     // Mark the clicked word as active AFTER updateTranscriptVisualState (which
@@ -736,12 +758,10 @@ class HyperaudioLite {
       target.parentNode.classList.add('active');
     }
 
-    if (!isNaN(timeSecs)) {
-      this.end = null;
-      this.myPlayer.setTime(timeSecs);
-      if (this.playOnClick) {
-        this.myPlayer.play();
-      }
+    this.end = null;
+    this.myPlayer.setTime(timeSecs);
+    if (this.playOnClick) {
+      this.myPlayer.play();
     }
   }
 
diff --git a/js/hyperaudio-lite.mjs b/js/hyperaudio-lite.mjs
index 82f9f7c..e24a79b 100644
--- a/js/hyperaudio-lite.mjs
+++ b/js/hyperaudio-lite.mjs
@@ -631,8 +631,23 @@ class HyperaudioLite {
 
   // Create an array of words with metadata from the transcript
   createWordArray(words) {
-    return Array.from(words).map(word => {
+    const wordArr = [];
+
+    Array.from(words).forEach(word => {
       const m = parseInt(word.getAttribute('data-m'));
+
+      // Reset to a clean baseline — stale read/active classes from a previous
+      // instance on the same DOM would survive the delta updates in
+      // updateTranscriptVisualState (#251).
+      word.classList.remove('read', 'active');
+      word.classList.add('unread');
+
+      // A malformed timestamp breaks every binary-search comparison that
+      // probes it. Keep the DOM node inert instead of poisoning playback.
+      if (Number.isNaN(m)) {
+        return;
+      }
+
       let p = word.parentNode;
       while (p !== document) {
         if (['p', 'figure', 'ul'].includes(p.tagName.toLowerCase())) {
@@ -640,13 +655,11 @@ class HyperaudioLite {
         }
         p = p.parentNode;
       }
-      // Reset to a clean baseline — stale read/active classes from a previous
-      // instance on the same DOM would survive the delta updates in
-      // updateTranscriptVisualState (#251).
-      word.classList.remove('read', 'active');
-      word.classList.add('unread');
-      return { n: word, m, p };
+
+      wordArr.push({ n: word, m, p });
     });
+
+    return wordArr;
   }
 
   getSelectionRange = () => {
@@ -721,10 +734,19 @@ class HyperaudioLite {
     }
 
     const target = e.target || e.srcElement;
+    const timeSecs = target && target.dataset
+      ? parseInt(target.dataset.m) / 1000
+      : NaN;
+
+    // Clicks on transcript whitespace or malformed timed nodes must not update
+    // the visual-state binary search with NaN.
+    if (Number.isNaN(timeSecs)) {
+      return;
+    }
+
     this.highlightedText = false;
     this.clearActiveClasses();
 
-    const timeSecs = parseInt(target.dataset.m) / 1000;
     this.updateTranscriptVisualState(timeSecs);
 
     // Mark the clicked word as active AFTER updateTranscriptVisualState (which
@@ -736,12 +758,10 @@ class HyperaudioLite {
       target.parentNode.classList.add('active');
     }
 
-    if (!isNaN(timeSecs)) {
-      this.end = null;
-      this.myPlayer.setTime(timeSecs);
-      if (this.playOnClick) {
-        this.myPlayer.play();
-      }
+    this.end = null;
+    this.myPlayer.setTime(timeSecs);
+    if (this.playOnClick) {
+      this.myPlayer.play();
     }
   }