diff --git a/jhdf/src/main/java/io/jhdf/checksum/ChecksumUtils.java b/jhdf/src/main/java/io/jhdf/checksum/ChecksumUtils.java
index 80650f33..15d39bd7 100644
--- a/jhdf/src/main/java/io/jhdf/checksum/ChecksumUtils.java
+++ b/jhdf/src/main/java/io/jhdf/checksum/ChecksumUtils.java
@@ -34,7 +34,26 @@ public static void validateChecksum(ByteBuffer buffer) {
 		if (calculatedChecksum != storedChecksum) {
 			throw new HdfChecksumMismatchException(storedChecksum, calculatedChecksum);
 		}
+	}
 
+	/**
+	 * Checks the next 4 bytes of the buffer are the the Jenkins Lookup 3 Checksum of the bytes between the mark and the
+	 * current position. The buffer position and mark are moved to after the checksum.
+	 *
+	 * @param buffer the buffer to check
+	 * @throws HdfChecksumMismatchException if the checksum is incorrect.
+	 */
+	public static void validateChecksumFromMark(ByteBuffer buffer) {
+		int position = buffer.position();
+		int end = buffer.reset().position(); // Move the buffer to the mark and get the new position
+		byte[] bytes = new byte[position - end];
+		buffer.get(bytes);
+		int calculatedChecksum = checksum(bytes);
+		int storedChecksum = buffer.getInt();
+		if (calculatedChecksum != storedChecksum) {
+			throw new HdfChecksumMismatchException(storedChecksum, calculatedChecksum);
+		}
+		buffer.mark();
 	}
 
 	public static int checksum(ByteBuffer buffer) {
diff --git a/jhdf/src/main/java/io/jhdf/dataset/chunked/indexing/FixedArrayIndex.java b/jhdf/src/main/java/io/jhdf/dataset/chunked/indexing/FixedArrayIndex.java
index f90a4d43..0ebe59fd 100644
--- a/jhdf/src/main/java/io/jhdf/dataset/chunked/indexing/FixedArrayIndex.java
+++ b/jhdf/src/main/java/io/jhdf/dataset/chunked/indexing/FixedArrayIndex.java
@@ -59,6 +59,7 @@ public FixedArrayIndex(HdfBackingStorage hdfBackingStorage, long address, Datase
 
 		final int headerSize = 12 + hdfBackingStorage.getSizeOfOffsets() + hdfBackingStorage.getSizeOfLengths();
 		final ByteBuffer bb = hdfBackingStorage.readBufferFromAddress(address, headerSize);
+		bb.mark();
 
 		byte[] formatSignatureBytes = new byte[4];
 		bb.get(formatSignatureBytes, 0, formatSignatureBytes.length);
@@ -85,14 +86,10 @@ public FixedArrayIndex(HdfBackingStorage hdfBackingStorage, long address, Datase
 		dataBlockAddress = Utils.readBytesAsUnsignedLong(bb, hdfBackingStorage.getSizeOfOffsets());
 
 		// Checksum
-		bb.rewind();
-		ChecksumUtils.validateChecksum(bb);
+		ChecksumUtils.validateChecksumFromMark(bb);
 
-		logger.info("Read fixed array index header. pages=[{}], maxEntries=[{}]", pages, maxNumberOfEntries);
-
-		// Building the object fills the chunks. Probably should be changed
-//		new FixedArrayDataBlock(this, hdfBackingStorage, dataBlockAddress);
 		dataBlockInitializer = new FixedArrayDataBlockInitializer(hdfBackingStorage);
+		logger.info("Read fixed array index header. pages=[{}], maxEntries=[{}]", pages, maxNumberOfEntries);
 	}
 
 	private class FixedArrayDataBlockInitializer extends LazyInitializer<FixedArrayDataBlock> {
@@ -117,13 +114,13 @@ private class FixedArrayDataBlock {
 
 		private FixedArrayDataBlock(FixedArrayIndex fixedArrayIndex, HdfBackingStorage hdfBackingStorage, long address) {
 
-			// TODO header size ignoring paging
 			int pageBitmapBytes = (pages + 7) / 8;
 			int headerSize = 6 + hdfBackingStorage.getSizeOfOffsets() + fixedArrayIndex.entrySize * fixedArrayIndex.maxNumberOfEntries + 4;
 			if(pages > 1) {
 				headerSize += pageBitmapBytes + (4 * pages);
 			}
 			final ByteBuffer bb = hdfBackingStorage.readBufferFromAddress(address, headerSize);
+			bb.mark();
 
 			byte[] formatSignatureBytes = new byte[4];
 			bb.get(formatSignatureBytes, 0, formatSignatureBytes.length);
@@ -139,8 +136,8 @@ private FixedArrayDataBlock(FixedArrayIndex fixedArrayIndex, HdfBackingStorage h
 				throw new HdfException("Unsupported fixed array data block version detected. Version: " + version);
 			}
 
-			final int clientId = bb.get();
-			if (clientId != fixedArrayIndex.clientId) {
+			final int dataBlockclientId = bb.get();
+			if (dataBlockclientId != fixedArrayIndex.clientId) {
 				throw new HdfException("Fixed array client ID mismatch. Possible file corruption detected");
 			}
 
@@ -150,56 +147,51 @@ private FixedArrayDataBlock(FixedArrayIndex fixedArrayIndex, HdfBackingStorage h
 			}
 
 			if(pages > 1) {
-//				throw new HdfException("Paged");
-//				pageBits
-//				pageBitmapSize = (pageCount + 7) / 8;
+				logger.info("Reading paged");
 				byte[] pageBitmap = new byte[pageBitmapBytes];
 				bb.get(pageBitmap);
-				// TODO skip check sum
-				bb.position(bb.position() + 4);
-//				bb.position(bb.position() + pageBitmapBytes );
+
+				ChecksumUtils.validateChecksumFromMark(bb);
 
 				int chunkIndex = 0;
 				for(int page = 0; page < pages; page++) {
-					final int pageSize;
+					final int currentPageSize;
 					if(page == pages -1) {
 						// last page so not a full page
-						pageSize = fixedArrayIndex.maxNumberOfEntries % fixedArrayIndex.pageSize;
+						currentPageSize = fixedArrayIndex.maxNumberOfEntries % fixedArrayIndex.pageSize;
 					} else {
-						pageSize = fixedArrayIndex.pageSize;
+						currentPageSize = fixedArrayIndex.pageSize;
 					}
 
-					if (clientId == 0) { // Not filtered
-						for (int i = 0; i < pageSize; i++) {
+					if (dataBlockclientId == 0) { // Not filtered
+						for (int i = 0; i < currentPageSize; i++) {
 							readUnfiltered(fixedArrayIndex, hdfBackingStorage.getSizeOfOffsets(), bb, chunkIndex++);
 						}
-					} else if (clientId == 1) { // Filtered
-						for (int i = 0; i < pageSize; i++) {
+					} else if (dataBlockclientId == 1) { // Filtered
+						for (int i = 0; i < currentPageSize; i++) {
 							readFiltered(fixedArrayIndex, hdfBackingStorage, bb, chunkIndex++);
 						}
 					} else {
-						throw new HdfException("Unrecognized client ID  = " + clientId);
+						throw new HdfException("Unrecognized client ID  = " + dataBlockclientId);
 					}
-
-					// TODO skip check sum
-					bb.position(bb.position() + 4);
+					ChecksumUtils.validateChecksumFromMark(bb);
 				}
 			} else {
 				// Unpaged
-				if (clientId == 0) { // Not filtered
+				logger.info("Reading unpaged");
+				if (dataBlockclientId == 0) { // Not filtered
 					for (int i = 0; i < fixedArrayIndex.maxNumberOfEntries; i++) {
 						readUnfiltered(fixedArrayIndex, hdfBackingStorage.getSizeOfOffsets(), bb, i);
 					}
-				} else if (clientId == 1) { // Filtered
+				} else if (dataBlockclientId == 1) { // Filtered
 					for (int i = 0; i < fixedArrayIndex.maxNumberOfEntries; i++) {
 						readFiltered(fixedArrayIndex, hdfBackingStorage, bb, i);
 					}
 				} else {
-					throw new HdfException("Unrecognized client ID  = " + clientId);
+					throw new HdfException("Unrecognized client ID  = " + dataBlockclientId);
 				}
 
-				bb.rewind();
-				ChecksumUtils.validateChecksum(bb);
+				ChecksumUtils.validateChecksumFromMark(bb);
 			}
 		}