diff --git a/src/app/features/genes/components/gene-comparison-tool/gene-comparison-tool.component.spec.ts b/src/app/features/genes/components/gene-comparison-tool/gene-comparison-tool.component.spec.ts
index add7e812..ff31aab3 100644
--- a/src/app/features/genes/components/gene-comparison-tool/gene-comparison-tool.component.spec.ts
+++ b/src/app/features/genes/components/gene-comparison-tool/gene-comparison-tool.component.spec.ts
@@ -520,13 +520,20 @@ describe('Component: GeneComparisonToolComponent', () => {
       expect(label2).toBe(expected2);
     });
 
-    it('should set circle size to zero for null/undefined pValues', () => {
+    it('should set circle size to zero for undefined pValues', () => {
       let tissue: GCTGeneTissue | undefined;
-      // null/undefined values should be zero
+      // undefined values should result in a circle size of zero
+      expect(tissue).toBeUndefined();
       const result = component.getCircleSize(tissue?.adj_p_val);
       expect(result).toBe(0);
     });
 
+    it('should set circle size to zero for null pValues', () => {
+      // null values should result in a circle size of zero pixels
+      const result = component.getCircleSize(null);
+      expect(result).toBe(0);
+    });
+
     it('should set circle size for pValues within acceptable ranges', () => {
       let expectedSizeInPixels = 0;
       let pValue = 0.5;
diff --git a/src/app/features/genes/components/gene-comparison-tool/gene-comparison-tool.component.ts b/src/app/features/genes/components/gene-comparison-tool/gene-comparison-tool.component.ts
index 3882c817..00856bcd 100644
--- a/src/app/features/genes/components/gene-comparison-tool/gene-comparison-tool.component.ts
+++ b/src/app/features/genes/components/gene-comparison-tool/gene-comparison-tool.component.ts
@@ -901,7 +901,7 @@ export class GeneComparisonToolComponent implements OnInit, AVI, OnDestroy {
     }
   }
 
-  getCircleSize(pval: number | undefined) {
+  getCircleSize(pval: number | null | undefined) {
     // define min and max size of possible circles in pixels
     const MIN_SIZE = 6;
     const MAX_SIZE = 50;