diff --git a/exomiser-core/src/main/java/org/monarchinitiative/exomiser/core/model/frequency/FrequencyData.java b/exomiser-core/src/main/java/org/monarchinitiative/exomiser/core/model/frequency/FrequencyData.java
index 6c11dd277..8b3cb47da 100644
--- a/exomiser-core/src/main/java/org/monarchinitiative/exomiser/core/model/frequency/FrequencyData.java
+++ b/exomiser-core/src/main/java/org/monarchinitiative/exomiser/core/model/frequency/FrequencyData.java
@@ -324,7 +324,7 @@ public float maxFreq() {
     @JsonIgnore
     @Nullable
     public Frequency maxFrequency() {
-        return this.size == 0 ? null : frequency(maxSource);
+        return maxSource == -1 ? null : frequency(maxSource);
     }
 
     /**
@@ -454,10 +454,11 @@ public Builder addFrequency(FrequencySource frequencySource, int ac, int an, int
          */
         private Builder addFrequency(FrequencySource frequencySource, float frequency, int ac, int an, int homCount) {
             frequencySources[frequencySource.ordinal()] = frequencySource;
-            frequencyData[frequencySource.ordinal() * WORD_SIZE + FREQ_OFFSET] = frequency;
-            frequencyData[frequencySource.ordinal() * WORD_SIZE + AC_OFFSET] = ac;
-            frequencyData[frequencySource.ordinal() * WORD_SIZE + AN_OFFSET] = an;
-            frequencyData[frequencySource.ordinal() * WORD_SIZE + HOM_OFFSET] = homCount;
+            int freqIndex = frequencySource.ordinal() * WORD_SIZE;
+            frequencyData[freqIndex + FREQ_OFFSET] = frequency;
+            frequencyData[freqIndex + AC_OFFSET] = ac;
+            frequencyData[freqIndex + AN_OFFSET] = an;
+            frequencyData[freqIndex + HOM_OFFSET] = homCount;
             return this;
         }
 
@@ -517,10 +518,12 @@ public FrequencyData build() {
                 FrequencySource source = values[i];
                 if (frequencySources[source.ordinal()] != null) {
                     sources[dataPos] = source;
-                    data[dataPos * WORD_SIZE + FREQ_OFFSET] = frequencyData[source.ordinal() * WORD_SIZE + FREQ_OFFSET];
-                    data[dataPos * WORD_SIZE + AC_OFFSET] = frequencyData[source.ordinal() * WORD_SIZE + AC_OFFSET];
-                    data[dataPos * WORD_SIZE + AN_OFFSET] = frequencyData[source.ordinal() * WORD_SIZE + AN_OFFSET];
-                    data[dataPos * WORD_SIZE + HOM_OFFSET] = frequencyData[source.ordinal() * WORD_SIZE + HOM_OFFSET];
+                    int dataIndex = dataPos * WORD_SIZE;
+                    int freqIndex = source.ordinal() * WORD_SIZE;
+                    data[dataIndex + FREQ_OFFSET] = frequencyData[freqIndex + FREQ_OFFSET];
+                    data[dataIndex + AC_OFFSET] = frequencyData[freqIndex + AC_OFFSET];
+                    data[dataIndex + AN_OFFSET] = frequencyData[freqIndex + AN_OFFSET];
+                    data[dataIndex + HOM_OFFSET] = frequencyData[freqIndex + HOM_OFFSET];
                     dataPos++;
                 }
             }
diff --git a/exomiser-core/src/test/java/org/monarchinitiative/exomiser/core/model/frequency/FrequencyDataTest.java b/exomiser-core/src/test/java/org/monarchinitiative/exomiser/core/model/frequency/FrequencyDataTest.java
index 1f09347aa..8db886462 100644
--- a/exomiser-core/src/test/java/org/monarchinitiative/exomiser/core/model/frequency/FrequencyDataTest.java
+++ b/exomiser-core/src/test/java/org/monarchinitiative/exomiser/core/model/frequency/FrequencyDataTest.java
@@ -26,12 +26,15 @@
 
 package org.monarchinitiative.exomiser.core.model.frequency;
 
+import org.h2.mvstore.MVStore;
+import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
+import org.monarchinitiative.exomiser.core.genome.dao.serialisers.MvStoreUtil;
+import org.monarchinitiative.exomiser.core.model.AlleleProtoAdaptor;
+import org.monarchinitiative.exomiser.core.proto.AlleleProto;
+import org.monarchinitiative.exomiser.core.proto.AlleleProtoFormatter;
 
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.List;
-import java.util.Set;
+import java.util.*;
 
 import static org.hamcrest.CoreMatchers.equalTo;
 import static org.hamcrest.CoreMatchers.is;
@@ -287,6 +290,17 @@ public void testGetMaxFrequencyWithData() {
         assertThat(instance.maxFrequency(), equalTo(maxFrequency));
     }
 
+    @Test
+    public void testGetMaxFrequencyWhenZeroData() {
+        Frequency maxFrequency = Frequency.of(GNOMAD_E_AFR, 0, 1000, 0);
+        Frequency minFrequency = Frequency.of(TOPMED, 0f);
+        FrequencyData instance = FrequencyData.of("rs545662810", minFrequency, maxFrequency);
+
+        assertThat(instance.maxFrequency(), equalTo(null));
+        assertThat(instance.maxFreq(), equalTo(0f));
+        assertThat(instance.frequencies(), equalTo(List.of(minFrequency, maxFrequency)));
+    }
+
     @Test
     public void testHasFrequencyOverPercentageValue() {
         float maxFreq = 0.05f;
@@ -482,12 +496,12 @@ void floatArray() {
         var an = 10000;
         var hom = 10;
         var af = Frequency.percentageFrequency(ac, an);
-        System.out.println("AF=" + af);
+
         data[0] = (float) ac;
         data[1] = (float) an;
         data[2] = (float) hom;
         data[3] = (float) af;
-        System.out.println("dataAF=" + data[3]);
+
         assertThat(Frequency.percentageFrequency((int) data[0], (int) data[1]), equalTo((float) data[3]));
     }