diff --git a/firmware/src/ad7172/adc.rs b/firmware/src/ad7172/adc.rs
index 5c87683..62a4115 100644
--- a/firmware/src/ad7172/adc.rs
+++ b/firmware/src/ad7172/adc.rs
@@ -114,7 +114,7 @@ impl<SPI: Transfer<u8>, NSS: OutputPin> Adc<SPI, NSS> {
     }
 
     /// Get data
-    pub fn read_data(&mut self) -> Result<u32, AdcError<SPI::Error>> {
+    pub fn read_data(&mut self) -> Result<i32, AdcError<SPI::Error>> {
         self.read_reg(&regs::Data)
             .map(|data| data.data())
     }
diff --git a/firmware/src/ad7172/regs.rs b/firmware/src/ad7172/regs.rs
index 4a9c23e..e96a066 100644
--- a/firmware/src/ad7172/regs.rs
+++ b/firmware/src/ad7172/regs.rs
@@ -145,10 +145,16 @@ impl if_mode::Data {
 
 def_reg!(Data, data, 0x04, 3);
 impl data::Data {
-    pub fn data(&self) -> u32 {
-        (u32::from(self.0[0]) << 16) |
-        (u32::from(self.0[1]) << 8) |
-        u32::from(self.0[2])
+    pub fn data(&self) -> i32 {
+        let raw =
+            (u32::from(self.0[0]) << 16) |
+            (u32::from(self.0[1]) << 8) |
+            u32::from(self.0[2]);
+        if raw & 0x80_0000 != 0 {
+            ((raw & 0x7F_FFFF) | 0x8000_0000) as i32
+        } else {
+            raw as i32
+        }
     }
 }