diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/bucket/BucketCache.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/bucket/BucketCache.java
index 2a8afa74fc7..58f32234d35 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/bucket/BucketCache.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/bucket/BucketCache.java
@@ -1285,8 +1285,8 @@ public class BucketCache implements BlockCache, HeapSize {
     }
 
     long offset() { // Java has no unsigned numbers
-      long o = ((long) offsetBase) & 0xFFFFFFFF;
-      o += (((long) (offset1)) & 0xFF) << 32;
+      long o = ((long) offsetBase) & 0xFFFFFFFFL; //This needs the L cast otherwise it will be sign extended as a negative number.
+      o += (((long) (offset1)) & 0xFF) << 32; //The 0xFF here does not need the L cast because it is treated as a positive int.
       return o << 8;
     }
 
diff --git a/hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/bucket/TestBucketCache.java b/hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/bucket/TestBucketCache.java
index 8cd665e3bf3..5a2a51cf420 100644
--- a/hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/bucket/TestBucketCache.java
+++ b/hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/bucket/TestBucketCache.java
@@ -388,4 +388,13 @@ public class TestBucketCache {
     long expectedOutput = (long) Math.floor(bucketCache.getAllocator().getTotalSize() * partitionFactor * minFactor);
     assertEquals(expectedOutput, bucketCache.getPartitionSize(partitionFactor));
   }
+
+  @Test
+  public void testOffsetProducesPositiveOutput() {
+    //This number is picked because it produces negative output if the values isn't ensured to be positive.
+    //See HBASE-18757 for more information.
+    long testValue = 549888460800L;
+    BucketCache.BucketEntry bucketEntry = new BucketCache.BucketEntry(testValue, 10, 10L, true);
+    assertEquals(testValue, bucketEntry.offset());
+  }
 }