diff --git a/index.ts b/index.ts
index efa4385..2c2a119 100644
--- a/index.ts
+++ b/index.ts
@@ -239,7 +239,7 @@ export function fieldsUnion<
       maybeEncodedCommonField = encodedFieldName;
     } else if (maybeEncodedCommonField !== encodedFieldName) {
       throw new Error(
-        `Codec.fieldsUnion: Variant at index ${index}: Key ${JSON.stringify(
+        `fieldsUnion: Variant at index ${index}: Key ${JSON.stringify(
           decodedCommonField,
         )}: Got a different encoded field name (${JSON.stringify(
           encodedFieldName,
@@ -252,7 +252,7 @@ export function fieldsUnion<
 
   if (typeof maybeEncodedCommonField !== "string") {
     throw new Error(
-      `Codec.fieldsUnion: Got unusable encoded common field: ${repr(
+      `fieldsUnion: Got unusable encoded common field: ${repr(
         maybeEncodedCommonField,
       )}`,
     );
diff --git a/tests/decoders.test.ts b/tests/decoders.test.ts
index afbe738..89e6a9b 100644
--- a/tests/decoders.test.ts
+++ b/tests/decoders.test.ts
@@ -642,7 +642,7 @@ describe("fieldsUnion", () => {
       //   Source has 0 element(s) but target requires 1.
       fieldsUnion("tag", []),
     ).toThrowErrorMatchingInlineSnapshot(
-      '"Codec.fieldsUnion: Got unusable encoded common field: undefined"',
+      '"fieldsUnion: Got unusable encoded common field: undefined"',
     );
   });
 
@@ -675,7 +675,7 @@ describe("fieldsUnion", () => {
         { tag: tag("B", { renameFieldFrom: "type" }) },
       ]),
     ).toThrowErrorMatchingInlineSnapshot(
-      '"Codec.fieldsUnion: Variant at index 1: Key \\"tag\\": Got a different encoded field name (\\"type\\") than before (\\"tag\\")."',
+      '"fieldsUnion: Variant at index 1: Key \\"tag\\": Got a different encoded field name (\\"type\\") than before (\\"tag\\")."',
     );
   });