diff --git a/src/sdam/topology_description.ts b/src/sdam/topology_description.ts
index d179339b3a..5867716822 100644
--- a/src/sdam/topology_description.ts
+++ b/src/sdam/topology_description.ts
@@ -362,29 +362,26 @@ function topologyTypeForServerType(serverType: ServerType): TopologyType {
   }
 }
 
+/**
+ * Compare objectIds. `null` is always less
+ * - `+1 = oid1 is greater than oid2`
+ * - `-1 = oid1 is less than oid2`
+ * - `+0 = oid1 is equal oid2`
+ */
 function compareObjectId(oid1?: ObjectId, oid2?: ObjectId): 0 | 1 | -1 {
-  if (oid1 == null) {
-    return oid2 == null ? 0 : -1;
-  }
-
-  if (oid2 == null) {
-    return 1;
+  if (oid1 == null && oid2 == null) {
+    return 0;
   }
 
-  const res = oid1.id.compare(oid2.id);
-  return res === 0 ? 0 : res > 0 ? 1 : -1;
-}
-
-function compareNumber(num1?: number, num2?: number): 0 | 1 | -1 {
-  if (num1 == null) {
-    return num2 == null ? 0 : -1;
+  if (oid1 == null) {
+    return -1;
   }
 
-  if (num2 == null) {
+  if (oid2 == null) {
     return 1;
   }
 
-  return num1 === num2 ? 0 : num1 > num2 ? 1 : -1;
+  return oid1.id.compare(oid2.id);
 }
 
 function updateRsFromPrimary(
@@ -403,21 +400,17 @@ function updateRsFromPrimary(
   const electionIdComparison = compareObjectId(maxElectionId, serverDescription.electionId);
   const maxElectionIdIsEqual = electionIdComparison === 0;
   const maxElectionIdIsLess = electionIdComparison === -1;
+  const maxSetVersionIsLessOrEqual = (maxSetVersion ?? -1) <= (serverDescription.setVersion ?? -1);
 
-  const setVersionComparison = compareNumber(maxSetVersion, serverDescription.setVersion);
-  const maxSetVersionIsLess = setVersionComparison === -1;
-  const maxSetVersionIsEqual = setVersionComparison === 0;
-
-  if (
-    maxElectionIdIsLess ||
-    (maxElectionIdIsEqual && (maxSetVersionIsLess || maxSetVersionIsEqual))
-  ) {
-    // We've seen a higher ElectionId! Update both!
-    // Or the electionId is the same but the setVersion increased
+  if (maxElectionIdIsLess || (maxElectionIdIsEqual && maxSetVersionIsLessOrEqual)) {
+    // The reported electionId was greater
+    // or the electionId was equal and reported setVersion was greater
+    // Always update both values, they are a tuple
     maxElectionId = serverDescription.electionId;
     maxSetVersion = serverDescription.setVersion;
   } else {
-    // this primary is stale, we must remove it
+    // Stale primary
+    // replace serverDescription with a default ServerDescription of type "Unknown"
     serverDescriptions.set(
       serverDescription.address,
       new ServerDescription(serverDescription.address)