diff --git a/daemon/clearpowerd/charge_control.py b/daemon/clearpowerd/charge_control.py
index 06a9dbb..acda9c0 100644
--- a/daemon/clearpowerd/charge_control.py
+++ b/daemon/clearpowerd/charge_control.py
@@ -68,11 +68,13 @@ def _write_thresholds(self, start, end):
             order = order[::-1]
         try:
             for path, value in order:
-                write_str(path, value)
+                if os.path.exists(path):
+                    write_str(path, value)
         except OSError:
             # firmware quirk: try the other order once before giving up
             for path, value in order[::-1]:
-                write_str(path, value)
+                if os.path.exists(path):
+                    write_str(path, value)
 
     def _write_behaviour(self, b):
         if not self.behaviour_supported:
diff --git a/daemon/clearpowerd/sampler.py b/daemon/clearpowerd/sampler.py
index 5cf9d7b..c6f65b3 100644
--- a/daemon/clearpowerd/sampler.py
+++ b/daemon/clearpowerd/sampler.py
@@ -107,7 +107,7 @@ def sample(self, hot=True):
         # ---- whole-machine draw ----
         if not on_ac and bat_w < -0.05:
             sys_w, sys_source = -bat_w, "battery"      # physical truth incl. all losses
-        elif psys > 0:
+        elif psys > 0 and (package <= 0 or psys >= package * 0.7):
             sys_w, sys_source = psys, "psys"
         elif package > 0:
             sys_w, sys_source = package + 3.0, "estimate"
diff --git a/daemon/clearpowerd/sources/rapl.py b/daemon/clearpowerd/sources/rapl.py
index e89a842..3c85b32 100644
--- a/daemon/clearpowerd/sources/rapl.py
+++ b/daemon/clearpowerd/sources/rapl.py
@@ -17,6 +17,8 @@ def __init__(self):
             if not name:
                 continue
             key = name.split("-")[0]  # package-0 -> package
+            if key == "psys" and read_int(os.path.join(d, "enabled")) == 0:
+                continue
             self.domains[key] = d
         self._wrap = {k: read_int(os.path.join(p, "max_energy_range_uj")) or (1 << 32)
                       for k, p in self.domains.items()}