diff --git a/src/graph/xml.cc b/src/graph/xml.cc
index c72d6c94f1..c14b538ae1 100644
--- a/src/graph/xml.cc
+++ b/src/graph/xml.cc
@@ -598,8 +598,8 @@ ncclResult_t ncclTopoGetXmlFromSys(struct ncclXmlNode* pciNode, struct ncclXml*
     NCCLCHECK(xmlGetAttrStr(pciNode, "busid", &newBusId));
     for (int s=0; s<parent->nSubs; s++) {
       const char* busId;
-      NCCLCHECK(xmlGetAttrStr(parent->subs[s], "busid", &busId));
-      if (strcmp(newBusId, busId) < 0) { subIndex = s; break; }
+      NCCLCHECK(xmlGetAttr(parent->subs[s], "busid", &busId));
+      if (busId != NULL && strcmp(newBusId, busId) < 0) { subIndex = s; break; }
     }
     for (int s = parent->nSubs; s > subIndex; s--) parent->subs[s] = parent->subs[s-1];
     parent->subs[subIndex] = pciNode;