diff --git a/ci/regression.sh b/ci/regression.sh
index b6125ce1..4a1336c8 100755
--- a/ci/regression.sh
+++ b/ci/regression.sh
@@ -56,6 +56,7 @@ echo "begin clustering tests..."
 ./ci/blackbox.sh --driver=rtlsim --cores=2 --l2cache --app=demo --args="-n1"
 ./ci/blackbox.sh --driver=rtlsim --cores=2 --clusters=2 --l3cache --app=demo --args="-n1"
 ./ci/blackbox.sh --driver=rtlsim --cores=2 --clusters=2 --l2cache --l3cache --app=io_addr --args="-n1"
+./ci/blackbox.sh --driver=simx --cores=4 --clusters=2 --l2cache --app=demo --args="-n1"
 ./ci/blackbox.sh --driver=simx --cores=4 --clusters=4 --l2cache --l3cache --app=demo --args="-n1"
 
 echo "clustering tests done!"
diff --git a/sim/simx/processor.cpp b/sim/simx/processor.cpp
index f069a6b7..6bb46229 100644
--- a/sim/simx/processor.cpp
+++ b/sim/simx/processor.cpp
@@ -109,7 +109,7 @@ Processor::Processor(const ArchDef& arch)
     }
 
     for (uint32_t j = 0; j < cores_per_cluster; ++j) {
-      auto& core = cores_.at((i * NUM_CLUSTERS) + j);        
+      auto& core = cores_.at((i * cores_per_cluster) + j);        
       cluster_mem_rsp_ports.at(j)->bind(&core->MemRspPort);
       core->MemReqPort.bind(cluster_mem_req_ports.at(j));
     }