diff --git a/datatypes.h b/datatypes.h
index 4969bdb8e131c20f273a0ac3223002d6a93d733f..646f643e5e173a1ea10a4201d0818bcad03875f5 100644
--- a/datatypes.h
+++ b/datatypes.h
@@ -81,7 +81,7 @@ typedef struct {
     float watt_hours;
     float watt_hours_charged;
     int32_t tachometer;
-    int tachometer_abs;
+    int32_t tachometer_abs;
     mc_fault_code fault_code;
 } mc_values;