diff --git a/proto/all_test.go b/proto/all_test.go
index 78181fd..4b29b27 100644
--- a/proto/all_test.go
+++ b/proto/all_test.go
@@ -37,7 +37,6 @@
 	"fmt"
 	"json"
 	"math"
-	"os"
 	"reflect"
 	"strings"
 	"testing"
@@ -430,7 +429,7 @@
 	err := o.Marshal(pb)
 	if err == nil {
 		t.Error("did not catch missing required fields")
-	} else if strings.Index(err.String(), "GoTest") < 0 {
+	} else if strings.Index(err.Error(), "GoTest") < 0 {
 		t.Error("wrong error type:", err)
 	}
 }
@@ -845,22 +844,22 @@
 
 	d, err := Marshal(pb)
 	if err != nil {
-		t.Errorf(err.String())
+		t.Error(err)
 	}
 
 	pbd := new(GoTest)
 	if err := Unmarshal(d, pbd); err != nil {
-		t.Errorf(err.String())
+		t.Error(err)
 	}
 
 	if pbd.F_BytesRequired == nil || len(pbd.F_BytesRequired) != 0 {
-		t.Errorf("required empty bytes field is incorrect")
+		t.Error("required empty bytes field is incorrect")
 	}
 	if pbd.F_BytesRepeated == nil || len(pbd.F_BytesRepeated) == 1 && pbd.F_BytesRepeated[0] == nil {
-		t.Errorf("repeated empty bytes field is incorrect")
+		t.Error("repeated empty bytes field is incorrect")
 	}
 	if pbd.F_BytesOptional == nil || len(pbd.F_BytesOptional) != 0 {
-		t.Errorf("optional empty bytes field is incorrect")
+		t.Error("optional empty bytes field is incorrect")
 	}
 }
 
@@ -874,16 +873,16 @@
 
 	d, err := Marshal(pb)
 	if err != nil {
-		t.Errorf(err.String())
+		t.Error(err)
 	}
 
 	pbd := new(GoTest)
 	if err := Unmarshal(d, pbd); err != nil {
-		t.Errorf(err.String())
+		t.Error(err)
 	}
 
 	if len(pbd.F_BytesRepeated) != 1 || pbd.F_BytesRepeated[0] == nil {
-		t.Errorf("Unexpected value for repeated bytes field")
+		t.Error("Unexpected value for repeated bytes field")
 	}
 }
 
@@ -1155,7 +1154,7 @@
 	_, err := Marshal(pb)
 	if err == nil {
 		t.Error("marshal: expected error, got nil")
-	} else if strings.Index(err.String(), "GoTestField") < 0 {
+	} else if strings.Index(err.Error(), "GoTestField") < 0 {
 		t.Errorf("marshal: bad error type: %v", err)
 	}
 
@@ -1166,7 +1165,7 @@
 	err = Unmarshal(buf, pb)
 	if err == nil {
 		t.Error("unmarshal: expected error, got nil")
-	} else if strings.Index(err.String(), "GoTestField") < 0 {
+	} else if strings.Index(err.Error(), "GoTestField") < 0 {
 		t.Errorf("unmarshal: bad error type: %v", err)
 	}
 }
@@ -1174,7 +1173,7 @@
 // A type that implements the Marshaler interface, but is not nillable.
 type nonNillableInt uint64
 
-func (nni nonNillableInt) Marshal() ([]byte, os.Error) {
+func (nni nonNillableInt) Marshal() ([]byte, error) {
 	return EncodeVarint(uint64(nni)), nil
 }
 
@@ -1187,7 +1186,7 @@
 	x uint64
 }
 
-func (nm *nillableMessage) Marshal() ([]byte, os.Error) {
+func (nm *nillableMessage) Marshal() ([]byte, error) {
 	return EncodeVarint(nm.x), nil
 }