diff --git a/healthd/BatteryMonitor.cpp b/healthd/BatteryMonitor.cpp
index e80f36855..bdf4aac4d 100644
--- a/healthd/BatteryMonitor.cpp
+++ b/healthd/BatteryMonitor.cpp
@@ -181,7 +181,7 @@ BatteryMonitor::PowerSupplyType BatteryMonitor::readPowerSupplyType(const String
         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;
     }