diff --git a/cmd/mda-lmtp/test_unix_failure.cmy b/cmd/mda-lmtp/test_unix_failure.cmy
index d5cd02c..ea925f5 100644
--- a/cmd/mda-lmtp/test_unix_failure.cmy
+++ b/cmd/mda-lmtp/test_unix_failure.cmy
@@ -26,6 +26,6 @@ nc <- .
 
 nc -> 452 Nananana
 
-mda <- Delivery failed remotely: 452 Nananana
+mda <- Delivery failed remotely: 452 "Nananana"
 mda wait 75
 
diff --git a/go.mod b/go.mod
index 58f77b8..1dc2950 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module blitiri.com.ar/go/chasquid
 
-go 1.25.0
+go 1.25.11
 
 require (
 	blitiri.com.ar/go/log v1.1.0
diff --git a/internal/smtpsrv/server_test.go b/internal/smtpsrv/server_test.go
index 7e7b815..bcea656 100644
--- a/internal/smtpsrv/server_test.go
+++ b/internal/smtpsrv/server_test.go
@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"net"
 	"net/smtp"
+	"net/textproto"
 	"os"
 	"strings"
 	"testing"
@@ -141,6 +142,23 @@ func sendEmailWithAuth(tb testing.TB, c *smtp.Client, auth smtp.Auth) {
 	localC.Wait()
 }
 
+// Checks err is a textproto.Error with the given code and message.
+func expectTPErr(tb testing.TB, err error, code int, msg string) {
+	tb.Helper()
+	if err == nil {
+		tb.Fatalf("Expected error %d %q, got nil", code, msg)
+	}
+	netErr, ok := err.(*textproto.Error)
+	if !ok {
+		tb.Fatalf("Expected textproto.Error(%d %q), got %T: %v",
+			code, msg, err, err)
+	}
+	if netErr.Code != code || netErr.Msg != msg {
+		tb.Fatalf("Expected textproto.Error(%d %q), got %d %q",
+			code, msg, netErr.Code, netErr.Msg)
+	}
+}
+
 func TestSimple(t *testing.T) {
 	c := mustDial(t, ModeSMTP, false)
 	defer c.Close()
@@ -203,11 +221,7 @@ func TestBrokenAuth(t *testing.T) {
 
 	auth := smtp.PlainAuth("", "user@broken", "passwd", "127.0.0.1")
 	err := c.Auth(auth)
-	if err == nil {
-		t.Errorf("Broken auth succeeded")
-	} else if err.Error() != "454 4.7.0 Temporary authentication failure" {
-		t.Errorf("Broken auth returned unexpected error %q", err.Error())
-	}
+	expectTPErr(t, err, 454, "4.7.0 Temporary authentication failure")
 }
 
 func TestWrongMailParsing(t *testing.T) {
@@ -300,9 +314,7 @@ func TestTooManyRecipients(t *testing.T) {
 	}
 
 	err := c.Rcpt("to102@somewhere")
-	if err == nil || err.Error() != "452 4.5.3 Too many recipients" {
-		t.Errorf("Expected too many recipients, got: %v", err)
-	}
+	expectTPErr(t, err, 452, "4.5.3 Too many recipients")
 }
 
 func TestRcptBrokenExists(t *testing.T) {
@@ -314,13 +326,7 @@ func TestRcptBrokenExists(t *testing.T) {
 	}
 
 	err := c.Rcpt("to@broken")
-	if err == nil {
-		t.Errorf("Accepted RCPT with broken Exists")
-	}
-	expect := "451 4.4.3 Temporary error checking address"
-	if err.Error() != expect {
-		t.Errorf("RCPT returned unexpected error %q", err.Error())
-	}
+	expectTPErr(t, err, 451, "4.4.3 Temporary error checking address")
 }
 
 func TestRcptUserDoesNotExist(t *testing.T) {
@@ -332,13 +338,8 @@ func TestRcptUserDoesNotExist(t *testing.T) {
 	}
 
 	err := c.Rcpt("doesnotexist@localhost")
-	if err == nil {
-		t.Errorf("Accepted RCPT for non-existent user")
-	}
-	expect := "550 5.1.1 Destination address is unknown (user does not exist)"
-	if err.Error() != expect {
-		t.Errorf("RCPT returned unexpected error %q", err.Error())
-	}
+	expectTPErr(t, err, 550,
+		"5.1.1 Destination address is unknown (user does not exist)")
 }
 
 var str1MiB string
@@ -392,9 +393,7 @@ func TestTooMuchData(t *testing.T) {
 	localC.Wait()
 
 	err = sendLargeEmail(t, c, maxDataSizeMiB+1)
-	if err == nil || err.Error() != "552 5.3.4 Message too big" {
-		t.Fatalf("Expected message too big, got: %v", err)
-	}
+	expectTPErr(t, err, 552, "5.3.4 Message too big")
 
 	// Repeat the test once again, the limit should not prevent connection
 	// from continuing.
diff --git a/test/t-10-hooks/run.sh b/test/t-10-hooks/run.sh
index eecc3fa..be252e4 100755
--- a/test/t-10-hooks/run.sh
+++ b/test/t-10-hooks/run.sh
@@ -54,7 +54,7 @@ check "SPF_PASS=0"
 if smtpc blockme@testserver < content >.logs/smtpc.log 2>&1; then
 	fail "ERROR: hook did not block email as expected"
 fi
-if ! grep -q "451 ¡No pasarán!" .logs/smtpc.log; then
+if ! grep -q '451 "¡No pasarán!"' .logs/smtpc.log; then
 	cat .logs/smtpc.log
 	fail "ERROR: transient hook error not returned correctly"
 fi
@@ -63,7 +63,7 @@ fi
 if smtpc permanent@testserver < content >.logs/smtpc.log 2>&1; then
 	fail "ERROR: hook did not block email as expected"
 fi
-if ! grep -q "554 Nos hacemos la permanente" .logs/smtpc.log; then
+if ! grep -q '554 "Nos hacemos la permanente"' .logs/smtpc.log; then
 	cat .logs/smtpc.log
 	fail "ERROR: permanent hook error not returned correctly"
 fi
diff --git a/test/t-16-spf/expected_dsn b/test/t-16-spf/expected_dsn
index 840632b..07d07c2 100644
--- a/test/t-16-spf/expected_dsn
+++ b/test/t-16-spf/expected_dsn
@@ -26,7 +26,7 @@ Delivery of your message to the following recipient(s) failed permanently:
 
 Technical details:
 - "userB@srv-b" (EMAIL) failed permanently with error:
-    MAIL+RCPT 550 5.7.23 SPF check failed: matched all
+    MAIL+RCPT 550 "5.7.23 SPF check failed: matched all"
 
 
 --???????????
@@ -40,7 +40,7 @@ Original-Recipient: utf-8; userB@srv-b
 Final-Recipient: utf-8; userB@srv-b
 Action: failed
 Status: 5.0.0
-Diagnostic-Code: smtp; MAIL+RCPT 550 5.7.23 SPF check failed: matched all
+Diagnostic-Code: smtp; MAIL+RCPT 550 "5.7.23 SPF check failed: matched all"