diff --git a/src/main/java/org/apache/commons/io/input/ReversedLinesFileReader.java b/src/main/java/org/apache/commons/io/input/ReversedLinesFileReader.java
index cd883af9adb..808769844c4 100644
--- a/src/main/java/org/apache/commons/io/input/ReversedLinesFileReader.java
+++ b/src/main/java/org/apache/commons/io/input/ReversedLinesFileReader.java
@@ -39,7 +39,9 @@
 import org.apache.commons.io.build.AbstractStreamBuilder;
 
 /**
- * Reads lines in a file reversely (similar to a BufferedReader, but starting at the last line). Useful for e.g. searching in log files.
+ * Reads lines in a file in reverse (similar to a BufferedReader, but starting at the last line).
+ * Line endings (\n, \r) are not included in the lines returned.
+ * Useful for e.g. searching in log files.
  * <p>
  * To build an instance, use {@link Builder}.
  * </p>
@@ -108,7 +110,7 @@ public ReversedLinesFileReader get() throws IOException {
     }
 
     private final class FilePart {
-        private final long no;
+        private final long partNumber;
 
         private final byte[] data;
 
@@ -119,20 +121,20 @@ private final class FilePart {
         /**
          * Constructs a new instance.
          *
-         * @param no                     the part number
+         * @param partNumber             the part number
          * @param length                 its length
          * @param leftOverOfLastFilePart remainder
          * @throws IOException if there is a problem reading the file
          */
-        private FilePart(final long no, final int length, final byte[] leftOverOfLastFilePart) throws IOException {
-            this.no = no;
+        private FilePart(final long partNumber, final int length, final byte[] leftOverOfLastFilePart) throws IOException {
+            this.partNumber = partNumber;
             final int dataLength = length + (leftOverOfLastFilePart != null ? leftOverOfLastFilePart.length : 0);
             this.data = new byte[dataLength];
-            final long off = (no - 1) * blockSize;
+            final long offset = (partNumber - 1) * blockSize;
 
             // read data
-            if (no > 0 /* file not empty */) {
-                channel.position(off);
+            if (partNumber > 0 /* file not empty */) {
+                channel.position(offset);
                 final int countRead = channel.read(ByteBuffer.wrap(data, 0, length));
                 if (countRead != length) {
                     throw new IllegalStateException("Count of requested bytes and actually read bytes don't match");
@@ -191,7 +193,7 @@ private String readLine() { //NOPMD Bug in PMD
             String line = null;
             int newLineMatchByteCount;
 
-            final boolean isLastFilePart = no == 1;
+            final boolean isLastFilePart = partNumber == 1;
 
             int i = currentLastBytePos;
             while (i > -1) {
@@ -252,8 +254,8 @@ private FilePart rollOver() throws IOException {
                         + "last readLine() should have returned something! currentLastCharPos=" + currentLastBytePos);
             }
 
-            if (no > 1) {
-                return new FilePart(no - 1, blockSize, leftOver);
+            if (partNumber > 1) {
+                return new FilePart(partNumber - 1, blockSize, leftOver);
             }
             // NO 1 was the last FilePart, we're finished
             if (leftOver != null) {
diff --git a/src/test/java/org/apache/commons/io/input/ReversedLinesFileReaderTestSimple.java b/src/test/java/org/apache/commons/io/input/ReversedLinesFileReaderTestSimple.java
index e8c5b0ecbb1..909404a6b49 100644
--- a/src/test/java/org/apache/commons/io/input/ReversedLinesFileReaderTestSimple.java
+++ b/src/test/java/org/apache/commons/io/input/ReversedLinesFileReaderTestSimple.java
@@ -34,11 +34,12 @@
 
 public class ReversedLinesFileReaderTestSimple {
 
+    private final int BLOCK_SIZE = 10;
+
     @Test
     public void testFileSizeIsExactMultipleOfBlockSize() throws URISyntaxException, IOException {
-        final int blockSize = 10;
         final File testFile20Bytes = TestResources.getFile("/test-file-20byteslength.bin");
-        try (ReversedLinesFileReader reversedLinesFileReader = new ReversedLinesFileReader(testFile20Bytes, blockSize,
+        try (ReversedLinesFileReader reversedLinesFileReader = new ReversedLinesFileReader(testFile20Bytes, BLOCK_SIZE,
                 StandardCharsets.ISO_8859_1.name())) {
             assertEqualsAndNoLineBreaks("987654321", reversedLinesFileReader.readLine());
             assertEqualsAndNoLineBreaks("123456789", reversedLinesFileReader.readLine());
@@ -47,9 +48,8 @@ public void testFileSizeIsExactMultipleOfBlockSize() throws URISyntaxException,
 
     @Test
     public void testLineCount() throws URISyntaxException, IOException {
-        final int blockSize = 10;
         final File testFile20Bytes = TestResources.getFile("/test-file-20byteslength.bin");
-        try (ReversedLinesFileReader reversedLinesFileReader = new ReversedLinesFileReader(testFile20Bytes, blockSize,
+        try (ReversedLinesFileReader reversedLinesFileReader = new ReversedLinesFileReader(testFile20Bytes, BLOCK_SIZE,
                 StandardCharsets.ISO_8859_1.name())) {
             assertThrows(IllegalArgumentException.class, () -> reversedLinesFileReader.readLines(-1));
             assertTrue(reversedLinesFileReader.readLines(0).isEmpty());
@@ -63,9 +63,8 @@ public void testLineCount() throws URISyntaxException, IOException {
 
     @Test
     public void testToString() throws URISyntaxException, IOException {
-        final int blockSize = 10;
         final File testFile20Bytes = TestResources.getFile("/test-file-20byteslength.bin");
-        try (ReversedLinesFileReader reversedLinesFileReader = new ReversedLinesFileReader(testFile20Bytes, blockSize,
+        try (ReversedLinesFileReader reversedLinesFileReader = new ReversedLinesFileReader(testFile20Bytes, BLOCK_SIZE,
                 StandardCharsets.ISO_8859_1.name())) {
             assertThrows(IllegalArgumentException.class, () -> reversedLinesFileReader.toString(-1));
             assertTrue(reversedLinesFileReader.readLines(0).isEmpty());
@@ -90,4 +89,17 @@ public void testUnsupportedEncodingUTF16() throws URISyntaxException {
             () -> new ReversedLinesFileReader(testFileEmpty, IOUtils.DEFAULT_BUFFER_SIZE, StandardCharsets.UTF_16.name()).close());
     }
 
+    @Test
+    // IO-639
+    public void testEmptyFirstLine() throws IOException, URISyntaxException {
+        final File testFileEmptyFirstLine = TestResources.getFile("/empty_first_line.bin");
+        try (ReversedLinesFileReader reversedLinesFileReader = new ReversedLinesFileReader(testFileEmptyFirstLine, BLOCK_SIZE,
+                StandardCharsets.US_ASCII.name())) {
+            assertEqualsAndNoLineBreaks("test2", reversedLinesFileReader.readLine());
+            assertEqualsAndNoLineBreaks("", reversedLinesFileReader.readLine());
+            assertEqualsAndNoLineBreaks("test1", reversedLinesFileReader.readLine());
+            assertEqualsAndNoLineBreaks("", reversedLinesFileReader.readLine());
+        }
+    }
+
 }
diff --git a/src/test/resources/org/apache/commons/io/empty_first_line.bin b/src/test/resources/org/apache/commons/io/empty_first_line.bin
new file mode 100644
index 00000000000..4e0e6422d38
--- /dev/null
+++ b/src/test/resources/org/apache/commons/io/empty_first_line.bin
@@ -0,0 +1,4 @@
+
+test1
+
+test2