diff --git a/src/main/java/org/apache/commons/collections4/bloomfilter/BloomFilter.java b/src/main/java/org/apache/commons/collections4/bloomfilter/BloomFilter.java
index acd5032643..f51eb081fc 100644
--- a/src/main/java/org/apache/commons/collections4/bloomfilter/BloomFilter.java
+++ b/src/main/java/org/apache/commons/collections4/bloomfilter/BloomFilter.java
@@ -305,6 +305,7 @@ default int estimateIntersection(final BloomFilter other) {
             // maximum estimate value using integer values is: 46144189292 thus
             // eThis + eOther can not overflow the long value.
             estimate = Math.round(eThis + eOther - eUnion);
+            estimate = estimate < 0 ? 0 : estimate;
         }
         return estimate>Integer.MAX_VALUE?Integer.MAX_VALUE:(int) estimate;
     }
diff --git a/src/test/java/org/apache/commons/collections4/bloomfilter/AbstractBloomFilterTest.java b/src/test/java/org/apache/commons/collections4/bloomfilter/AbstractBloomFilterTest.java
index 4b5a275e57..5e9d91a186 100644
--- a/src/test/java/org/apache/commons/collections4/bloomfilter/AbstractBloomFilterTest.java
+++ b/src/test/java/org/apache/commons/collections4/bloomfilter/AbstractBloomFilterTest.java
@@ -214,6 +214,17 @@ public void testClear() {
         assertEquals(0, bf1.cardinality());
     }
 
+    @Test
+    public final void testNegativeIntersection() {
+        IndexProducer p1 = IndexProducer.fromIndexArray(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 20, 26, 28, 30, 32, 34, 35, 36, 37, 39, 40, 41, 42, 43, 45, 46, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71);
+        IndexProducer p2 = IndexProducer.fromIndexArray(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27);
+
+        BloomFilter filter1 = createEmptyFilter(Shape.fromKM(17, 72));
+        filter1.merge(p1);
+        BloomFilter filter2 = createEmptyFilter(Shape.fromKM(17, 72));
+        filter2.merge(p2);
+        assertEquals(0, filter1.estimateIntersection(filter2));
+    }
     /**
      * Tests that the estimated intersection calculations are correct.
      */
@@ -424,11 +435,11 @@ public void testBitMapProducerSize() {
     /**
      * Testing class returns the value as the only value.
      */
-    class BadHasher implements Hasher {
+    public static class BadHasher implements Hasher {
 
         IndexProducer producer;
 
-        BadHasher(final int value) {
+        public BadHasher(final int value) {
             this.producer = IndexProducer.fromIndexArray(new int[] {value});
         }
 
diff --git a/src/test/java/org/apache/commons/collections4/bloomfilter/ArrayHasher.java b/src/test/java/org/apache/commons/collections4/bloomfilter/ArrayHasher.java
index 84e223ddbf..f2a18c426a 100644
--- a/src/test/java/org/apache/commons/collections4/bloomfilter/ArrayHasher.java
+++ b/src/test/java/org/apache/commons/collections4/bloomfilter/ArrayHasher.java
@@ -24,10 +24,10 @@
  *
  * <p>To be used for testing only.</p>
  */
-final class ArrayHasher implements Hasher {
+public final class ArrayHasher implements Hasher {
     private final int[] values;
 
-    ArrayHasher(final int... values) {
+    public ArrayHasher(final int... values) {
         this.values = values;
     }
 
diff --git a/src/test/java/org/apache/commons/collections4/bloomfilter/DefaultIndexProducerTest.java b/src/test/java/org/apache/commons/collections4/bloomfilter/DefaultIndexProducerTest.java
index c09158c355..2682a96a7e 100644
--- a/src/test/java/org/apache/commons/collections4/bloomfilter/DefaultIndexProducerTest.java
+++ b/src/test/java/org/apache/commons/collections4/bloomfilter/DefaultIndexProducerTest.java
@@ -74,7 +74,7 @@ protected int getForEachIndexBehaviour() {
      * @param bound the upper bound (exclusive) of the values in the array.
      * @return an array of int.
      */
-    static int[] generateIntArray(final int size, final int bound) {
+    public static int[] generateIntArray(final int size, final int bound) {
         return ThreadLocalRandom.current().ints(size, 0, bound).toArray();
     }
 
@@ -83,7 +83,7 @@ static int[] generateIntArray(final int size, final int bound) {
      * @param ary the array
      * @return the set.
      */
-    static BitSet uniqueSet(final int[] ary) {
+    public static BitSet uniqueSet(final int[] ary) {
         final BitSet bs = new BitSet();
         Arrays.stream(ary).forEach(bs::set);
         return bs;
@@ -94,7 +94,7 @@ static BitSet uniqueSet(final int[] ary) {
      * @param ary the array to sort and make unique
      * @return the sorted unique array.
      */
-    static int[] unique(final int[] ary) {
+    public static int[] unique(final int[] ary) {
         return Arrays.stream(ary).distinct().sorted().toArray();
     }
 
diff --git a/src/test/java/org/apache/commons/collections4/bloomfilter/IncrementingHasher.java b/src/test/java/org/apache/commons/collections4/bloomfilter/IncrementingHasher.java
index ac0fd5111b..a680ac565e 100644
--- a/src/test/java/org/apache/commons/collections4/bloomfilter/IncrementingHasher.java
+++ b/src/test/java/org/apache/commons/collections4/bloomfilter/IncrementingHasher.java
@@ -25,7 +25,7 @@
  *
  * <p>To be used for testing only.</p>
  */
-final class IncrementingHasher implements Hasher {
+public final class IncrementingHasher implements Hasher {
 
     /**
      * The initial hash value.
@@ -46,7 +46,7 @@ final class IncrementingHasher implements Hasher {
      * @param initial The initial value for the hasher.
      * @param increment The value to increment the hash by on each iteration.
      */
-    IncrementingHasher(final long initial, final long increment) {
+    public IncrementingHasher(final long initial, final long increment) {
         this.initial = initial;
         this.increment = increment;
     }
diff --git a/src/test/java/org/apache/commons/collections4/bloomfilter/TestingHashers.java b/src/test/java/org/apache/commons/collections4/bloomfilter/TestingHashers.java
index 8589000fbb..27a13fd7c4 100644
--- a/src/test/java/org/apache/commons/collections4/bloomfilter/TestingHashers.java
+++ b/src/test/java/org/apache/commons/collections4/bloomfilter/TestingHashers.java
@@ -18,16 +18,16 @@
 /**
  * A collection of methods and statics that represent standard hashers in testing.
  */
-class TestingHashers {
+public class TestingHashers {
     /**
      * Hasher that increments from 1.
      */
-    static final Hasher FROM1 = new IncrementingHasher(1, 1);
+    public static final Hasher FROM1 = new IncrementingHasher(1, 1);
 
     /**
      * Hasher that increments from 11.
      */
-    static final Hasher FROM11 = new IncrementingHasher(11, 1);
+    public static final Hasher FROM11 = new IncrementingHasher(11, 1);
 
     /**
      * Do not instantiate.
@@ -41,7 +41,7 @@ private TestingHashers() {}
      * @param hashers The hashers to merge
      * @return {@code filter} for chaining
      */
-    static <T extends BloomFilter> T mergeHashers(T filter, Hasher...hashers) {
+    public static <T extends BloomFilter> T mergeHashers(T filter, Hasher...hashers) {
         for (Hasher h : hashers) {
             filter.merge(h);
         }
@@ -54,7 +54,7 @@ static <T extends BloomFilter> T mergeHashers(T filter, Hasher...hashers) {
      * @param filter The Bloom filter to populate
      * @return {@code filter} for chaining
      */
-    static <T extends BloomFilter> T populateFromHashersFrom1AndFrom11(T filter) {
+    public static <T extends BloomFilter> T populateFromHashersFrom1AndFrom11(T filter) {
         return mergeHashers(filter, FROM1, FROM11);
     }
 
@@ -64,7 +64,7 @@ static <T extends BloomFilter> T populateFromHashersFrom1AndFrom11(T filter) {
      * @param filter the Bloom filter to populate
      * @return {@code filter} for chaining
      */
-    static <T extends BloomFilter> T populateEntireFilter(T filter) {
+    public static <T extends BloomFilter> T populateEntireFilter(T filter) {
         int n = filter.getShape().getNumberOfBits();
         int k = filter.getShape().getNumberOfHashFunctions();
         for (int i = 0; i < n; i += k) {