diff --git a/dtt/ds1621.c b/dtt/ds1621.c
index bf30e9c..4948181 100644
--- a/dtt/ds1621.c
+++ b/dtt/ds1621.c
@@ -85,7 +85,7 @@
      * Calculate sensor address and register.
      *
      */
-    sensor = DTT_I2C_DEV_CODE + (sensor & sensor);
+    sensor = DTT_I2C_DEV_CODE + (sensor & 0x07);
 
     /*
      * Handle various data sizes.