diff --git a/checkin_notes b/checkin_notes
index 9f18743099..f654e3f175 100644
--- a/checkin_notes
+++ b/checkin_notes
@@ -8596,3 +8596,16 @@ Charlie 2 Dec 2010
         PostInstall.cpp
         release_boinc.sh
         WaitPermissions.cpp
+
+David  2 Dec 2010
+    - client: fix scheduling bug.
+        The round-robin simulation wasn't handling multithread jobs correctly.
+        For example, given two 3-CPU jobs,
+        it would model running them together on a 4-CPU host.
+        This doesn't correspond with the CPU scheduler,
+        which runs only 1 at a time.
+        So the simulator would say that there are no idle CPUs
+        when in fact there are, and no new CPU jobs would be fetched.
+
+    client/
+        rr_sim.cpp
diff --git a/client/rr_sim.cpp b/client/rr_sim.cpp
index 59f3c57224..550f5de7fe 100644
--- a/client/rr_sim.cpp
+++ b/client/rr_sim.cpp
@@ -290,7 +290,7 @@ void CLIENT_STATE::rr_simulation() {
             }
         } else {
             p->cpu_pwf.has_runnable_jobs = true;
-            if (p->cpu_pwf.sim_nused < ncpus) {
+            if (p->cpu_pwf.sim_nused + rp->avp->avg_ncpus <= ncpus) {
                 sim_status.activate(rp, 0);
                 p->rr_sim_status.activate(rp);
             } else {
@@ -447,9 +447,9 @@ void CLIENT_STATE::rr_simulation() {
             }
         } else {
             while (1) {
-                if (pbest->cpu_pwf.sim_nused >= ncpus) break;
                 RESULT* rp = pbest->rr_sim_status.get_pending();
                 if (!rp) break;
+                if (pbest->cpu_pwf.sim_nused + rp->avp->avg_ncpus > ncpus) break;
                 sim_status.activate(rp, sim_now-now);
                 pbest->rr_sim_status.activate(rp);
             }