diff --git a/data/src/main/kotlin/voice/data/Chapter.kt b/data/src/main/kotlin/voice/data/Chapter.kt
index b128829ad6..6d660d3528 100644
--- a/data/src/main/kotlin/voice/data/Chapter.kt
+++ b/data/src/main/kotlin/voice/data/Chapter.kt
@@ -27,14 +27,30 @@ data class Chapter(
   val chapterMarks: List<ChapterMark> = if (markData.isEmpty()) {
     listOf(ChapterMark(name, 0L, duration))
   } else {
-    val sorted = markData.sorted()
-    sorted.mapIndexed { index, (startMs, name) ->
-      val isFirst = index == 0
-      val isLast = index == sorted.size - 1
-      val start = if (isFirst) 0L else startMs
-      val end = if (isLast) duration else sorted[index + 1].startMs - 1
-      ChapterMark(name = name, startMs = start, endMs = end)
+    val sorted = markData.distinctBy { it.startMs }
+      .filter { it.startMs in 0..<duration }
+      .sorted()
+    val result = mutableListOf<ChapterMark>()
+    for ((index, markData) in sorted.withIndex()) {
+      val name = markData.name
+      val previous = result.lastOrNull()
+      val next = sorted.getOrNull(index + 1)
+      val startMs = if (previous == null) 0L else previous.endMs + 1
+      val endMs = if (next != null && next.startMs + 2 < duration && startMs < next.startMs - 1) {
+        next.startMs - 1
+      } else {
+        duration - 1
+      }
+      result += ChapterMark(
+        name = name,
+        startMs = startMs,
+        endMs = endMs,
+      )
+      if (endMs == duration - 1) {
+        break
+      }
     }
+    result.ifEmpty { listOf(ChapterMark(name, 0L, duration)) }
   }
 
   override fun compareTo(other: Chapter): Int {
diff --git a/data/src/main/kotlin/voice/data/ChapterMark.kt b/data/src/main/kotlin/voice/data/ChapterMark.kt
index 2d4e7f8d36..26f630d238 100644
--- a/data/src/main/kotlin/voice/data/ChapterMark.kt
+++ b/data/src/main/kotlin/voice/data/ChapterMark.kt
@@ -20,6 +20,12 @@ data class ChapterMark(
   val endMs: Long,
 ) {
 
+  init {
+    require(startMs < endMs) {
+      "Start must be less than end in $this"
+    }
+  }
+
   operator fun contains(position: Duration): Boolean = position.inWholeMilliseconds in startMs..endMs
   operator fun contains(positionMs: Long): Boolean = positionMs in startMs..endMs
 }
diff --git a/data/src/test/kotlin/voice/data/ChapterTest.kt b/data/src/test/kotlin/voice/data/ChapterTest.kt
new file mode 100644
index 0000000000..7d9564dcb7
--- /dev/null
+++ b/data/src/test/kotlin/voice/data/ChapterTest.kt
@@ -0,0 +1,31 @@
+package voice.data
+
+import io.kotest.matchers.collections.shouldContainInOrder
+import org.junit.Test
+import java.time.Instant
+
+class ChapterTest {
+
+  @Test
+  fun `chapter parsing does best effort on broken marks`() {
+    val positions = Chapter(
+      duration = 20L,
+      fileLastModified = Instant.now(),
+      id = ChapterId(""),
+      markData = listOf(11, 5, 5, 10).mapIndexed { index, i ->
+        MarkData(
+          startMs = i.toLong(),
+          name = "Mark $index",
+        )
+      },
+      name = "Chapter",
+    ).chapterMarks.map { MarkPosition(it.startMs, it.endMs) }
+
+    positions.shouldContainInOrder(
+      MarkPosition(0L, 9L),
+      MarkPosition(10L, 19L),
+    )
+  }
+
+  data class MarkPosition(val start: Long, val end: Long)
+}
diff --git a/playbackScreen/src/main/kotlin/voice/playbackScreen/BookPlayViewState.kt b/playbackScreen/src/main/kotlin/voice/playbackScreen/BookPlayViewState.kt
index 38995a5665..50956ce15f 100644
--- a/playbackScreen/src/main/kotlin/voice/playbackScreen/BookPlayViewState.kt
+++ b/playbackScreen/src/main/kotlin/voice/playbackScreen/BookPlayViewState.kt
@@ -17,7 +17,14 @@ data class BookPlayViewState(
   val playing: Boolean,
   val cover: ImmutableFile?,
   val skipSilence: Boolean,
-)
+) {
+
+  init {
+    require(duration > Duration.ZERO) {
+      "Duration must be positive in $this"
+    }
+  }
+}
 
 internal sealed interface BookPlayDialogViewState {
   data class SpeedDialog(