diff --git a/healthd/BatteryMonitor.cpp b/healthd/BatteryMonitor.cpp
index 9e168e9..1c388f2 100644
--- a/healthd/BatteryMonitor.cpp
+++ b/healthd/BatteryMonitor.cpp
@@ -168,7 +168,7 @@
         return ANDROID_POWER_SUPPLY_TYPE_UNKNOWN;
 
     auto ret = mapSysfsString(buf.c_str(), supplyTypeMap);
-    if (ret < 0) {
+    if (!ret) {
         KLOG_WARNING(LOG_TAG, "Unknown power supply type '%s'\n", buf.c_str());
         *ret = ANDROID_POWER_SUPPLY_TYPE_UNKNOWN;
     }