diff --git a/extras/tsl2561/tsl2561.c b/extras/tsl2561/tsl2561.c
index d17c074..b4dc9b5 100644
--- a/extras/tsl2561/tsl2561.c
+++ b/extras/tsl2561/tsl2561.c
@@ -362,7 +362,7 @@ bool tsl2561_read_lux(tsl2561_t *device, uint32_t *lux)
             break;
     }
 
-    uint32_t temp;
+    int32_t temp;
     temp = ((channel0 * b) - (channel1 * m));
 
     // Do not allow negative lux value