diff --git a/src/main/java/de/hottis/mbusMaster/MbusDevice.java b/src/main/java/de/hottis/mbusMaster/MbusDevice.java
index 18aa237..1736e95 100644
--- a/src/main/java/de/hottis/mbusMaster/MbusDevice.java
+++ b/src/main/java/de/hottis/mbusMaster/MbusDevice.java
@@ -66,7 +66,7 @@ abstract public class MbusDevice {
   }
 
   public double getErrorRatio() {
-    return this.errorCnt / this.successCnt;
+    return this.errorCnt / (this.successCnt + this.errorCnt);
   }
 
   public void parse(byte[] frame) throws MbusException {