diff --git a/internal/impl/codec_field.go b/internal/impl/codec_field.go
index 35d4002..cb4b482 100644
--- a/internal/impl/codec_field.go
+++ b/internal/impl/codec_field.go
@@ -10,6 +10,7 @@
 	"sync"
 
 	"google.golang.org/protobuf/encoding/protowire"
+	"google.golang.org/protobuf/internal/errors"
 	"google.golang.org/protobuf/proto"
 	pref "google.golang.org/protobuf/reflect/protoreflect"
 	preg "google.golang.org/protobuf/reflect/protoregistry"
@@ -20,6 +21,7 @@
 
 func (errInvalidUTF8) Error() string     { return "string field contains invalid UTF-8" }
 func (errInvalidUTF8) InvalidUTF8() bool { return true }
+func (errInvalidUTF8) Unwrap() error     { return errors.Error }
 
 // initOneofFieldCoders initializes the fast-path functions for the fields in a oneof.
 //
diff --git a/proto/decode_test.go b/proto/decode_test.go
index 3f64dd4..1b2f216 100644
--- a/proto/decode_test.go
+++ b/proto/decode_test.go
@@ -15,6 +15,7 @@
 	"google.golang.org/protobuf/reflect/protoreflect"
 	"google.golang.org/protobuf/testing/protopack"
 
+	"google.golang.org/protobuf/internal/errors"
 	testpb "google.golang.org/protobuf/internal/testprotos/test"
 	test3pb "google.golang.org/protobuf/internal/testprotos/test3"
 )
@@ -82,6 +83,8 @@
 				got := want.ProtoReflect().New().Interface()
 				if err := opts.Unmarshal(test.wire, got); err == nil {
 					t.Errorf("Unmarshal unexpectedly succeeded\ninput bytes: [%x]\nMessage:\n%v", test.wire, prototext.Format(got))
+				} else if !errors.Is(err, proto.Error) {
+					t.Errorf("Unmarshal error is not a proto.Error: %v", err)
 				}
 			})
 		}
diff --git a/proto/encode_test.go b/proto/encode_test.go
index 3915c9d..967def7 100644
--- a/proto/encode_test.go
+++ b/proto/encode_test.go
@@ -18,6 +18,7 @@
 	"google.golang.org/protobuf/proto"
 	pref "google.golang.org/protobuf/reflect/protoreflect"
 
+	"google.golang.org/protobuf/internal/errors"
 	orderpb "google.golang.org/protobuf/internal/testprotos/order"
 	testpb "google.golang.org/protobuf/internal/testprotos/test"
 	test3pb "google.golang.org/protobuf/internal/testprotos/test3"
@@ -136,6 +137,9 @@
 				if err == nil {
 					t.Fatalf("Marshal unexpectedly succeeded\noutput bytes: [%x]\nMessage:\n%v", got, prototext.Format(m))
 				}
+				if !errors.Is(err, proto.Error) {
+					t.Fatalf("Marshal error is not a proto.Error: %v", err)
+				}
 			})
 		}
 	}