diff --git a/internal/extsvc/clublog.go b/internal/extsvc/clublog.go
index c0719a2..66bce77 100644
--- a/internal/extsvc/clublog.go
+++ b/internal/extsvc/clublog.go
@@ -27,6 +27,14 @@ const clublogBatchURL = "https://clublog.org/putlogs.php"
 // must send a real, app-identifying User-Agent.
 const clublogUserAgent = "OpsLog/1.0 (+https://github.com/GregTroar/OpsLog)"
 
+// looksLikeHTML reports a body that is a web page rather than an answer. Club
+// Log serves its normal site for refusals and blocks, so this is what separates
+// "here is what went wrong" from 4 KB of markup an operator cannot act on.
+func looksLikeHTML(s string) bool {
+	l := strings.ToLower(strings.TrimSpace(s))
+	return strings.HasPrefix(l, "<!doctype html") || strings.HasPrefix(l, "<html")
+}
+
 // clublogDownloadURL is Club Log's ADIF export. Used ONLY to verify credentials
 // (see TestClublog): it is the one authenticated endpoint that cannot change
 // anything in the operator's log, which is what a test button must never do.
@@ -244,10 +252,12 @@ func TestClublog(ctx context.Context, cfg ServiceConfig) (string, error) {
 	form.Set("email", email)
 	form.Set("password", cfg.Password)
 	form.Set("call", call)
-	// A future start date: the credentials are what is being checked, not the
-	// log, and an operator with 130 000 QSOs should not download them to find
-	// out whether a password is right.
-	form.Set("startyear", "2099")
+	// No date filter. A "startyear=2099" was tried to keep the reply small, but
+	// Club Log answers an unrecognised request with the SAME 403 it uses for a
+	// refused login — so an unverified parameter would have made every correct
+	// password look wrong, which is the failure this whole change exists to end.
+	// The reply is capped at 4 KB and the body closed immediately instead; the
+	// status code arrives before any of it.
 
 	req, err := http.NewRequestWithContext(ctx, http.MethodPost, clublogDownloadURL, strings.NewReader(form.Encode()))
 	if err != nil {
@@ -268,11 +278,18 @@ func TestClublog(ctx context.Context, cfg ServiceConfig) (string, error) {
 	case http.StatusOK:
 		return fmt.Sprintf("Ready — %s via %s (Club Log accepted the login)", call, email), nil
 	case http.StatusUnauthorized, http.StatusForbidden:
-		if msg == "" {
-			msg = "wrong e-mail, password or logbook callsign"
-		}
-		return "", fmt.Errorf("Club Log rejected the login: %s", msg)
+		// Club Log refuses with its ordinary web page, not an error string, so the
+		// body is 4 KB of markup that says nothing to an operator. It goes to the
+		// log — that is where a real diagnosis happens — and the message says the
+		// one thing there is to do about it.
+		LogSink("clublog: login refused (http %d), body: %s", resp.StatusCode, msg)
+		return "", fmt.Errorf("Club Log refused the login — check the account e-mail, " +
+			"the password and the logbook callsign. They are the Club Log website's own credentials")
 	default:
+		LogSink("clublog: unexpected http %d, body: %s", resp.StatusCode, msg)
+		if looksLikeHTML(msg) {
+			return "", fmt.Errorf("clublog: Club Log answered with a web page (http %d) instead of a log — see the log file", resp.StatusCode)
+		}
 		if len(msg) > 200 {
 			msg = msg[:200] + "…"
 		}
diff --git a/internal/extsvc/clublog_test.go b/internal/extsvc/clublog_test.go
new file mode 100644
index 0000000..709f592
--- /dev/null
+++ b/internal/extsvc/clublog_test.go
@@ -0,0 +1,26 @@
+package extsvc
+
+import "testing"
+
+// Club Log answers a refused login with its ordinary web page. The operator must
+// get a sentence they can act on, not four kilobytes of markup — that was the
+// first thing reported once the test started working at all.
+func TestLooksLikeHTML(t *testing.T) {
+	cases := []struct {
+		body string
+		want bool
+	}{
+		{"<!DOCTYPE html>\n<html lang='en'>…403 - Access denied…", true},
+		{"  <html><head><title>403</title></head></html>", true},
+		{"<HTML>", true},
+		{"Invalid credentials", false},
+		{"", false},
+		// An ADIF answer must never be mistaken for a page.
+		{"<eoh>\n<call:5>F4BPO <band:3>20m <eor>", false},
+	}
+	for _, c := range cases {
+		if got := looksLikeHTML(c.body); got != c.want {
+			t.Errorf("looksLikeHTML(%.40q) = %v, want %v", c.body, got, c.want)
+		}
+	}
+}
