diff --git a/drivers/iio/light/si1133.c b/drivers/iio/light/si1133.c
index 015a21f0c2ef41..9174ab9288808a 100644
--- a/drivers/iio/light/si1133.c
+++ b/drivers/iio/light/si1133.c
@@ -102,6 +102,9 @@
 #define SI1133_INPUT_FRACTION_LOW	15
 #define SI1133_LUX_OUTPUT_FRACTION	12
 #define SI1133_LUX_BUFFER_SIZE		9
+#define SI1133_MEASURE_BUFFER_SIZE	3
+
+#define SI1133_SIGN_BIT_INDEX 23
 
 static const int si1133_scale_available[] = {
 	1, 2, 4, 8, 16, 32, 64, 128};
@@ -234,13 +237,13 @@ static const struct si1133_lux_coeff lux_coeff = {
 	}
 };
 
-static int si1133_calculate_polynomial_inner(u32 input, u8 fraction, u16 mag,
+static int si1133_calculate_polynomial_inner(s32 input, u8 fraction, u16 mag,
 					     s8 shift)
 {
 	return ((input << fraction) / mag) << shift;
 }
 
-static int si1133_calculate_output(u32 x, u32 y, u8 x_order, u8 y_order,
+static int si1133_calculate_output(s32 x, s32 y, u8 x_order, u8 y_order,
 				   u8 input_fraction, s8 sign,
 				   const struct si1133_coeff *coeffs)
 {
@@ -276,7 +279,7 @@ static int si1133_calculate_output(u32 x, u32 y, u8 x_order, u8 y_order,
  * The algorithm is from:
  * https://siliconlabs.github.io/Gecko_SDK_Doc/efm32zg/html/si1133_8c_source.html#l00716
  */
-static int si1133_calc_polynomial(u32 x, u32 y, u8 input_fraction, u8 num_coeff,
+static int si1133_calc_polynomial(s32 x, s32 y, u8 input_fraction, u8 num_coeff,
 				  const struct si1133_coeff *coeffs)
 {
 	u8 x_order, y_order;
@@ -614,7 +617,7 @@ static int si1133_measure(struct si1133_data *data,
 {
 	int err;
 
-	__be16 resp;
+	u8 buffer[SI1133_MEASURE_BUFFER_SIZE];
 
 	err = si1133_set_adcmux(data, 0, chan->channel);
 	if (err)
@@ -625,12 +628,13 @@ static int si1133_measure(struct si1133_data *data,
 	if (err)
 		return err;
 
-	err = si1133_bulk_read(data, SI1133_REG_HOSTOUT(0), sizeof(resp),
-			       (u8 *)&resp);
+	err = si1133_bulk_read(data, SI1133_REG_HOSTOUT(0), sizeof(buffer),
+			       buffer);
 	if (err)
 		return err;
 
-	*val = be16_to_cpu(resp);
+	*val = sign_extend32((buffer[0] << 16) | (buffer[1] << 8) | buffer[2],
+			     SI1133_SIGN_BIT_INDEX);
 
 	return err;
 }
@@ -704,9 +708,9 @@ static int si1133_get_lux(struct si1133_data *data, int *val)
 {
 	int err;
 	int lux;
-	u32 high_vis;
-	u32 low_vis;
-	u32 ir;
+	s32 high_vis;
+	s32 low_vis;
+	s32 ir;
 	u8 buffer[SI1133_LUX_BUFFER_SIZE];
 
 	/* Activate lux channels */
@@ -719,9 +723,16 @@ static int si1133_get_lux(struct si1133_data *data, int *val)
 	if (err)
 		return err;
 
-	high_vis = (buffer[0] << 16) | (buffer[1] << 8) | buffer[2];
-	low_vis = (buffer[3] << 16) | (buffer[4] << 8) | buffer[5];
-	ir = (buffer[6] << 16) | (buffer[7] << 8) | buffer[8];
+	high_vis =
+		sign_extend32((buffer[0] << 16) | (buffer[1] << 8) | buffer[2],
+			      SI1133_SIGN_BIT_INDEX);
+
+	low_vis =
+		sign_extend32((buffer[3] << 16) | (buffer[4] << 8) | buffer[5],
+			      SI1133_SIGN_BIT_INDEX);
+
+	ir = sign_extend32((buffer[6] << 16) | (buffer[7] << 8) | buffer[8],
+			   SI1133_SIGN_BIT_INDEX);
 
 	if (high_vis > SI1133_ADC_THRESHOLD || ir > SI1133_ADC_THRESHOLD)
 		lux = si1133_calc_polynomial(high_vis, ir,