diff --git a/core/src/main/scala/org/apache/spark/api/java/JavaPairRDD.scala b/core/src/main/scala/org/apache/spark/api/java/JavaPairRDD.scala
index 9419c3f5989be..7dcfbf741c4f1 100644
--- a/core/src/main/scala/org/apache/spark/api/java/JavaPairRDD.scala
+++ b/core/src/main/scala/org/apache/spark/api/java/JavaPairRDD.scala
@@ -678,7 +678,7 @@ class JavaPairRDD[K, V](val rdd: RDD[(K, V)])
    * <a href="http://dx.doi.org/10.1145/2452376.2452456">here</a>.
    *
    * @param relativeSD Relative accuracy. Smaller values create counters that require more space.
-   *                   It should be greater than 0.000017.
+   *                   It must be greater than 0.000017.
    * @param partitioner partitioner of the resulting RDD.
    */
   def countApproxDistinctByKey(relativeSD: Double, partitioner: Partitioner): JavaPairRDD[K, Long] =
@@ -694,7 +694,7 @@ class JavaPairRDD[K, V](val rdd: RDD[(K, V)])
    * <a href="http://dx.doi.org/10.1145/2452376.2452456">here</a>.
    *
    * @param relativeSD Relative accuracy. Smaller values create counters that require more space.
-   *                   It should be greater than 0.000017.
+   *                   It must be greater than 0.000017.
    * @param numPartitions number of partitions of the resulting RDD.
    */
   def countApproxDistinctByKey(relativeSD: Double, numPartitions: Int): JavaPairRDD[K, Long] = {
@@ -709,7 +709,7 @@ class JavaPairRDD[K, V](val rdd: RDD[(K, V)])
    * <a href="http://dx.doi.org/10.1145/2452376.2452456">here</a>.
    *
    * @param relativeSD Relative accuracy. Smaller values create counters that require more space.
-   *                   It should be greater than 0.000017.
+   *                   It must be greater than 0.000017.
    */
   def countApproxDistinctByKey(relativeSD: Double): JavaPairRDD[K, Long] = {
     fromRDD(rdd.countApproxDistinctByKey(relativeSD))
diff --git a/core/src/main/scala/org/apache/spark/api/java/JavaRDDLike.scala b/core/src/main/scala/org/apache/spark/api/java/JavaRDDLike.scala
index 2741532732c27..330569a8d8837 100644
--- a/core/src/main/scala/org/apache/spark/api/java/JavaRDDLike.scala
+++ b/core/src/main/scala/org/apache/spark/api/java/JavaRDDLike.scala
@@ -565,7 +565,7 @@ trait JavaRDDLike[T, This <: JavaRDDLike[T, This]] extends Serializable {
    * <a href="http://dx.doi.org/10.1145/2452376.2452456">here</a>.
    *
    * @param relativeSD Relative accuracy. Smaller values create counters that require more space.
-   *                   It should be greater than 0.000017.
+   *                   It must be greater than 0.000017.
    */
   def countApproxDistinct(relativeSD: Double): Long = rdd.countApproxDistinct(relativeSD)
 
diff --git a/core/src/main/scala/org/apache/spark/rdd/PairRDDFunctions.scala b/core/src/main/scala/org/apache/spark/rdd/PairRDDFunctions.scala
index d459815ae7cbe..f2ce3cbd47f93 100644
--- a/core/src/main/scala/org/apache/spark/rdd/PairRDDFunctions.scala
+++ b/core/src/main/scala/org/apache/spark/rdd/PairRDDFunctions.scala
@@ -225,16 +225,16 @@ class PairRDDFunctions[K, V](self: RDD[(K, V)])
    * would trigger sparse representation of registers, which may reduce the memory consumption
    * and increase accuracy when the cardinality is small.
    *
-   *@param p The precision value for the normal set.
-   *          `p` must be a value between 4 and `sp` (32 max).
+   * @param p The precision value for the normal set.
+   *          `p` must be a value between 4 and `sp` if `sp` is not zero (32 max).
    * @param sp The precision value for the sparse set, between 0 and 32.
    *           If `sp` equals 0, the sparse representation is skipped.
    * @param partitioner Partitioner to use for the resulting RDD.
    */
   @Experimental
   def countApproxDistinctByKey(p: Int, sp: Int, partitioner: Partitioner): RDD[(K, Long)] = {
-    require(p >= 4, s"p ($p) should be >= 4")
-    require(sp <= 32, s"sp ($sp) should be <= 32")
+    require(p >= 4, s"p ($p) must be >= 4")
+    require(sp <= 32, s"sp ($sp) must be <= 32")
     require(sp == 0 || p <= sp, s"p ($p) cannot be greater than sp ($sp)")
     val createHLL = (v: V) => {
       val hll = new HyperLogLogPlus(p, sp)
@@ -261,11 +261,11 @@ class PairRDDFunctions[K, V](self: RDD[(K, V)])
    * <a href="http://dx.doi.org/10.1145/2452376.2452456">here</a>.
    *
    * @param relativeSD Relative accuracy. Smaller values create counters that require more space.
-   *                   It should be greater than 0.000017.
+   *                   It must be greater than 0.000017.
    * @param partitioner partitioner of the resulting RDD
    */
   def countApproxDistinctByKey(relativeSD: Double, partitioner: Partitioner): RDD[(K, Long)] = {
-    require(relativeSD > 0.000017, s"accuracy ($relativeSD) should be greater than 0.000017")
+    require(relativeSD > 0.000017, s"accuracy ($relativeSD) must be greater than 0.000017")
     val p = math.ceil(2.0 * math.log(1.054 / relativeSD) / math.log(2)).toInt
     assert(p <= 32)
     countApproxDistinctByKey(if (p < 4) 4 else p, 0, partitioner)
@@ -279,7 +279,7 @@ class PairRDDFunctions[K, V](self: RDD[(K, V)])
    * <a href="http://dx.doi.org/10.1145/2452376.2452456">here</a>.
    *
    * @param relativeSD Relative accuracy. Smaller values create counters that require more space.
-   *                   It should be greater than 0.000017.
+   *                   It must be greater than 0.000017.
    * @param numPartitions number of partitions of the resulting RDD
    */
   def countApproxDistinctByKey(relativeSD: Double, numPartitions: Int): RDD[(K, Long)] = {
@@ -294,7 +294,7 @@ class PairRDDFunctions[K, V](self: RDD[(K, V)])
    * <a href="http://dx.doi.org/10.1145/2452376.2452456">here</a>.
    *
    * @param relativeSD Relative accuracy. Smaller values create counters that require more space.
-   *                   It should be greater than 0.000017.
+   *                   It must be greater than 0.000017.
    */
   def countApproxDistinctByKey(relativeSD: Double = 0.05): RDD[(K, Long)] = {
     countApproxDistinctByKey(relativeSD, defaultPartitioner(self))
diff --git a/core/src/main/scala/org/apache/spark/rdd/RDD.scala b/core/src/main/scala/org/apache/spark/rdd/RDD.scala
index 58375b9b07c32..585b2f76afa65 100644
--- a/core/src/main/scala/org/apache/spark/rdd/RDD.scala
+++ b/core/src/main/scala/org/apache/spark/rdd/RDD.scala
@@ -929,9 +929,9 @@ abstract class RDD[T: ClassTag](
    * and increase accuracy when the cardinality is small.
    *
    * @param p The precision value for the normal set.
-   *          <code>p</code> must be a value between 4 and <code>sp</code>.
+   *          `p` must be a value between 4 and `sp` if `sp` is not zero (32 max).
    * @param sp The precision value for the sparse set, between 0 and 32.
-   *           If <code>sp</code> equals 0, the sparse representation is skipped.
+   *           If `sp` equals 0, the sparse representation is skipped.
    */
   @Experimental
   def countApproxDistinct(p: Int, sp: Int): Long = {
@@ -958,6 +958,7 @@ abstract class RDD[T: ClassTag](
    * <a href="http://dx.doi.org/10.1145/2452376.2452456">here</a>.
    *
    * @param relativeSD Relative accuracy. Smaller values create counters that require more space.
+   *                   It must be greater than 0.000017.
    */
   def countApproxDistinct(relativeSD: Double = 0.05): Long = {
     val p = math.ceil(2.0 * math.log(1.054 / relativeSD) / math.log(2)).toInt