diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/util/healthconnect/HealthConnectUtils.kt b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/util/healthconnect/HealthConnectUtils.kt
index 2a23698f5e..5380597d7b 100755
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/util/healthconnect/HealthConnectUtils.kt
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/util/healthconnect/HealthConnectUtils.kt
@@ -242,6 +242,7 @@ class HealthConnectUtils {
         val manager = GBApplication.app().deviceManager
         val syncIntervalInSeconds: Long = 24 * 60 * 60 // 1 day slices
         val lookBackInSeconds: Long = 24 * 60 * 60
+        val sleepLookForwardSeconds: Long = 12 * 60 * 60
 
         for (targetAddress in selectedDevices) {
             // Check if worker has been cancelled
@@ -363,14 +364,19 @@ class HealthConnectUtils {
                     updateSyncStatus(summary, true, summaryCallback, mainHandler)
 
                     val queryStartTs = currentSliceStartTs.minusSeconds(lookBackInSeconds)
-                    LOG.info("$HC_SYNC_TAG Querying Gadgetbridge DB for {}({}) from {} to {}", gbDevice.aliasOrName, dataType.name, queryStartTs, currentSliceEndTs)
+                    val queryEndTs = if (dataType == HealthConnectPermissionManager.HealthConnectDataType.SLEEP) {
+                        currentSliceEndTs.plusSeconds(sleepLookForwardSeconds)
+                    } else {
+                        currentSliceEndTs
+                    }
+                    LOG.info("$HC_SYNC_TAG Querying Gadgetbridge DB for {}({}) from {} to {}", gbDevice.aliasOrName, dataType.name, queryStartTs, queryEndTs)
 
                     // Fetch activityBasedSamples under their own lock if needed for the current dataType
                     val activityBasedSamples: List<ActivitySample>? = 
                         if (dataType == HealthConnectPermissionManager.HealthConnectDataType.ACTIVITY || 
                             dataType == HealthConnectPermissionManager.HealthConnectDataType.SLEEP) {
                             GBApplication.acquireDbReadOnly().use { db ->
-                                getActivitySamples(db, gbDevice, queryStartTs.epochSecond.toInt(), currentSliceEndTs.epochSecond.toInt())
+                                getActivitySamples(db, gbDevice, queryStartTs.epochSecond.toInt(), queryEndTs.epochSecond.toInt())
                             }
                         } else {
                             null
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/util/healthconnect/syncers/SleepSyncer.kt b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/util/healthconnect/syncers/SleepSyncer.kt
index 992f82d2b0..541d85971f 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/util/healthconnect/syncers/SleepSyncer.kt
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/util/healthconnect/syncers/SleepSyncer.kt
@@ -123,11 +123,14 @@ internal object SleepSyncer : ContextualActivitySampleSyncer {
         val sessionBoundaryStart = analysisSession.sleepStart.toInstant()
         val sessionBoundaryEndInclusive = analysisSession.sleepEnd.toInstant()
 
-        // Check if session overlaps with the current slice (inclusive boundaries [sliceStart, sliceEnd])
-        // Skip if: sessionStart > sliceEnd OR sessionEnd < sliceStart
-        if (sessionBoundaryStart.isAfter(sliceEndBoundary) || sessionBoundaryEndInclusive.isBefore(sliceStartBoundary)) {
+        // Only process this session if its START falls within the current slice [sliceStart, sliceEnd).
+        // The look-back query ensures full session data is available even for sessions starting near the
+        // previous slice boundary. The look-forward query ensures full session data for sessions starting
+        // near the current slice end. This ownership rule prevents duplicate records when the same session
+        // is discovered across multiple slices due to the look-back overlap.
+        if (sessionBoundaryStart.isBefore(sliceStartBoundary) || !sessionBoundaryStart.isBefore(sliceEndBoundary)) {
             LOG.debug(
-                "Skipping sleep session (identified by SleepAnalysis) for device '{}' (Timeframe: {} to {}) as it does not overlap with current slice ({} to {}).",
+                "Skipping sleep session (identified by SleepAnalysis) for device '{}' (Timeframe: {} to {}) as its start does not fall within current slice [{} to {}).",
                 deviceName,
                 sessionBoundaryStart,
                 sessionBoundaryEndInclusive,