diff --git a/CHANGELOG.md b/CHANGELOG.md
index ab8e4c514e..6f39d04d84 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,8 @@
 # Unreleased changes
 
+* General
+  * BUGFIX: fix `int32` to `ErrorType` mapping. ([#1063](https://github.com/mozilla/glean/pull/1063))
+
 [Full changelog](https://github.com/mozilla/glean/compare/v31.4.0...main)
 
 # v31.4.0 (2020-07-16)
diff --git a/glean-core/src/error_recording.rs b/glean-core/src/error_recording.rs
index e5fd6fdb8c..73f3eb8239 100644
--- a/glean-core/src/error_recording.rs
+++ b/glean-core/src/error_recording.rs
@@ -26,7 +26,7 @@ use crate::Lifetime;
 /// Note: the cases in this enum must be kept in sync with the ones
 /// in the platform-specific code (e.g. ErrorType.kt) and with the
 /// metrics in the registry files.
-#[derive(Debug)]
+#[derive(Debug, PartialEq)]
 pub enum ErrorType {
     /// For when the value to be recorded does not match the metric-specific restrictions
     InvalidValue,
@@ -58,7 +58,7 @@ impl TryFrom<i32> for ErrorType {
             0 => Ok(ErrorType::InvalidValue),
             1 => Ok(ErrorType::InvalidLabel),
             2 => Ok(ErrorType::InvalidState),
-            4 => Ok(ErrorType::InvalidOverflow),
+            3 => Ok(ErrorType::InvalidOverflow),
             e => Err(ErrorKind::Lifetime(e).into()),
         }
     }
@@ -155,6 +155,18 @@ mod test {
     use crate::metrics::*;
     use crate::tests::new_glean;
 
+    #[test]
+    fn error_type_i32_mapping() {
+        let error: ErrorType = std::convert::TryFrom::try_from(0).unwrap();
+        assert_eq!(error, ErrorType::InvalidValue);
+        let error: ErrorType = std::convert::TryFrom::try_from(1).unwrap();
+        assert_eq!(error, ErrorType::InvalidLabel);
+        let error: ErrorType = std::convert::TryFrom::try_from(2).unwrap();
+        assert_eq!(error, ErrorType::InvalidState);
+        let error: ErrorType = std::convert::TryFrom::try_from(3).unwrap();
+        assert_eq!(error, ErrorType::InvalidOverflow);
+    }
+
     #[test]
     fn recording_of_all_error_types() {
         let (glean, _t) = new_glean(None);