diff --git a/Civi/Api4/Query/Api4SelectQuery.php b/Civi/Api4/Query/Api4SelectQuery.php
index 922f0954a203..a5aa319ac806 100644
--- a/Civi/Api4/Query/Api4SelectQuery.php
+++ b/Civi/Api4/Query/Api4SelectQuery.php
@@ -535,7 +535,8 @@ private function addExplicitJoins() {
       $side = array_shift($join) ? 'INNER' : 'LEFT';
       // Add all fields from joined entity to spec
       $joinEntityGet = \Civi\API\Request::create($entity, 'get', ['version' => 4, 'checkPermissions' => $this->getCheckPermissions()]);
-      foreach ($joinEntityGet->entityFields() as $field) {
+      $joinEntityFields = $joinEntityGet->entityFields();
+      foreach ($joinEntityFields as $field) {
         $field['sql_name'] = '`' . $alias . '`.`' . $field['column_name'] . '`';
         $this->addSpecField($alias . '.' . $field['name'], $field);
       }
@@ -543,7 +544,7 @@ private function addExplicitJoins() {
         $conditions = $this->getBridgeJoin($join, $entity, $alias);
       }
       else {
-        $conditions = $this->getJoinConditions($join, $entity, $alias);
+        $conditions = $this->getJoinConditions($join, $entity, $alias, $joinEntityFields);
       }
       foreach (array_filter($join) as $clause) {
         $conditions[] = $this->treeWalkClauses($clause, 'ON');
@@ -559,20 +560,29 @@ private function addExplicitJoins() {
    * @param array $joinTree
    * @param string $joinEntity
    * @param string $alias
+   * @param array $joinEntityFields
    * @return array
    */
-  private function getJoinConditions($joinTree, $joinEntity, $alias) {
+  private function getJoinConditions($joinTree, $joinEntity, $alias, $joinEntityFields) {
     $conditions = [];
     // getAclClause() expects a stack of 1-to-1 join fields to help it dedupe, but this is more flexible,
     // so unless this is a direct 1-to-1 join with the main entity, we'll just hack it
     // with a padded empty stack to bypass its deduping.
     $stack = [NULL, NULL];
-    // If we're not explicitly referencing the joinEntity ID in the ON clause, search for a default
-    $explicitId = array_filter($joinTree, function($clause) use ($alias) {
+    // If we're not explicitly referencing the ID (or some other FK field) of the joinEntity in the ON clause, search for a default
+    $explicitFK = array_filter($joinTree, function($clause) use ($alias, $joinEntityFields) {
       list($sideA, $op, $sideB) = array_pad((array) $clause, 3, NULL);
-      return $op === '=' && ($sideA === "$alias.id" || $sideB === "$alias.id");
+      if ($op !== '=' || !$sideB) {
+        return FALSE;
+      }
+      foreach ([$sideA, $sideB] as $expr) {
+        if ($expr === "$alias.id" || !empty($joinEntityFields["$alias.$expr"]['fk_entity'])) {
+          return TRUE;
+        }
+      }
+      return FALSE;
     });
-    if (!$explicitId) {
+    if (!$explicitFK) {
       foreach ($this->apiFieldSpec as $name => $field) {
         if ($field['entity'] !== $joinEntity && $field['fk_entity'] === $joinEntity) {
           $conditions[] = $this->treeWalkClauses([$name, '=', "$alias.id"], 'ON');