diff --git a/main.go b/main.go
index acc61f2..c10c108 100644
--- a/main.go
+++ b/main.go
@@ -106,7 +106,10 @@ func readRegs(client modbus.Client, start, qty uint16) {
 		if addr <= start || addr > start+qty {
 			continue
 		}
-		val := reg.read(data[(addr-start-1)*2:])
+		val, err := reg.read(data[(addr-start-1)*2:])
+		if err != nil {
+			log.Fatalf("Couldn't parse input register data: %v", err)
+		}
 		//fmt.Printf("%s: %v %s\n", reg.name, val, reg.unit)
 		registerGauges[addr].Set(val)
 	}
diff --git a/modbus.go b/modbus.go
index f5e2d71..cae503c 100644
--- a/modbus.go
+++ b/modbus.go
@@ -1,23 +1,36 @@
 package main
 
-import "encoding/binary"
+import (
+	"encoding/binary"
+	"fmt"
+)
 
 // Helpers for converting straight from modbus data to floats.
 
-func u16(data []byte) float64 {
-	return float64(binary.BigEndian.Uint16(data))
+func u16(data []byte) (float64, error) {
+	n := binary.BigEndian.Uint16(data)
+	if n == 0xFFFF {
+		// probably a misread
+		return 0, fmt.Errorf("likely misread: u16 read %v", n)
+	}
+	return float64(n), nil
 }
 
-func s16(data []byte) float64 {
-	return float64(int16(binary.BigEndian.Uint16(data)))
+func s16(data []byte) (float64, error) {
+	return float64(int16(binary.BigEndian.Uint16(data))), nil
 }
 
-func u32(data []byte) float64 {
+func u32(data []byte) (float64, error) {
 	// Little-endian big-endian :#
-	return float64(uint32(binary.BigEndian.Uint16(data)) + uint32(binary.BigEndian.Uint16(data[2:]))<<16)
+	n := uint32(binary.BigEndian.Uint16(data)) + uint32(binary.BigEndian.Uint16(data[2:]))<<16
+	if n == 0xFFFFFFFF {
+		// probably a misread
+		return 0, fmt.Errorf("likely misread: u32 read %v", n)
+	}
+	return float64(n), nil
 }
 
-func s32(data []byte) float64 {
+func s32(data []byte) (float64, error) {
 	// Little-endian big-endian :#
-	return float64(int32(binary.BigEndian.Uint16(data)) + int32(binary.BigEndian.Uint16(data[2:]))<<16)
+	return float64(int32(binary.BigEndian.Uint16(data)) + int32(binary.BigEndian.Uint16(data[2:]))<<16), nil
 }
diff --git a/sungrow_map.go b/sungrow_map.go
index fb72216..cd460be 100644
--- a/sungrow_map.go
+++ b/sungrow_map.go
@@ -2,13 +2,14 @@ package main
 
 type register struct {
 	name string
-	conv func([]byte) float64
+	conv func([]byte) (float64, error)
 	mult float64
 	unit string
 }
 
-func (r *register) read(data []byte) float64 {
-	return r.conv(data) * r.mult
+func (r *register) read(data []byte) (float64, error) {
+	n, err := r.conv(data)
+	return n * r.mult, err
 }
 
 var sungrowInputRegs = map[uint16]*register{
@@ -32,7 +33,7 @@ var sungrowInputRegs = map[uint16]*register{
 	//5023: {"phase_b_current", u16, 0.1, "A"},
 	//5024: {"phase_c_current", u16, 0.1, "A"},
 	5031: {"output_real_power", u32, 1, "VA"},
-	5033: {"output_reactive_power", s32, 1, "VA"},
+	5033: {"output_reactive_power", s32, 1, "VAr"},
 	5035: {"power_factor", s16, 0.001, ""},
 	5036: {"frequency", u16, 0.1, "Hz"},
 	5049: {"nominal_reactive_power", s16, 0.1, "kVA"},