diff --git a/cmd/mavweb/main.go b/cmd/mavweb/main.go
index 87b3665..09aa456 100644
--- a/cmd/mavweb/main.go
+++ b/cmd/mavweb/main.go
@@ -1540,7 +1540,13 @@ func handlePTT(w http.ResponseWriter, r *http.Request, voiceAddr string, session
 			return
 		}
 		w.Header().Set("Content-Type", "audio/l16;rate=16000;channels=1")
-		w.Header().Set("X-Reply-Text", url.QueryEscape(pttResp.ReplyText))
+		// PathEscape, not QueryEscape (Vikunja #533). QueryEscape writes a space
+		// as "+", which is form encoding, and the client decodes this header
+		// with decodeURIComponent, which only knows "%20" — so every space in a
+		// spoken reply reached the on-page log as a plus sign. PathEscape is the
+		// flavour decodeURIComponent actually reverses, which keeps the encoding
+		// a property of the header rather than something the client has to know.
+		w.Header().Set("X-Reply-Text", url.PathEscape(pttResp.ReplyText))
 		w.Write(pttResp.ReplyAudio.Bytes)
 		return
 	}
diff --git a/cmd/mavweb/replytext_test.go b/cmd/mavweb/replytext_test.go
new file mode 100644
index 0000000..233c946
--- /dev/null
+++ b/cmd/mavweb/replytext_test.go
@@ -0,0 +1,59 @@
+package main
+
+import (
+	"net/url"
+	"strings"
+	"testing"
+)
+
+// decodeURIComponent is what static/app.js calls on X-Reply-Text. PathUnescape
+// is its Go equivalent for this purpose: both turn %XX into bytes and both
+// leave a literal "+" alone. That last part is the whole defect — QueryEscape
+// wrote spaces as "+" and the client had no way to tell those from a plus the
+// speaker actually said.
+func decodeURIComponent(t *testing.T, s string) string {
+	t.Helper()
+	out, err := url.PathUnescape(s)
+	if err != nil {
+		t.Fatalf("decodeURIComponent(%q): %v", s, err)
+	}
+	return out
+}
+
+// The reply the QA session actually saw was "на+04.08.2026+ничего+нет."
+// (Vikunja #533). Round-tripping through the client's decoder is the assertion
+// that matters — checking the encoder in isolation would have passed with
+// QueryEscape too.
+func TestReplyTextSurvivesTheClientDecoder(t *testing.T) {
+	cases := []string{
+		"на 04.08.2026 ничего нет.",
+		"Я поставила тебе напоминание позвонить маме через час.",
+		// A literal plus must stay a plus, which is the case that makes
+		// "just replace + with space on the JS side" the wrong fix.
+		"два плюс два = 2+2",
+		// Headers cannot carry a raw newline. PathEscape writes %0A.
+		"первая строка\nвторая строка",
+		"", // no reply text at all
+	}
+	for _, want := range cases {
+		encoded := url.PathEscape(want)
+		if strings.ContainsAny(encoded, "\r\n") {
+			t.Errorf("encoded %q contains a raw newline, which is not a legal header value", want)
+		}
+		if got := decodeURIComponent(t, encoded); got != want {
+			t.Errorf("round trip: got %q, want %q", got, want)
+		}
+	}
+}
+
+// The specific regression, named. QueryEscape is form encoding and this header
+// is not a form.
+func TestReplyTextDoesNotUseFormEncoding(t *testing.T) {
+	const spoken = "на 04.08.2026 ничего нет."
+	if got := decodeURIComponent(t, url.QueryEscape(spoken)); got == spoken {
+		t.Skip("QueryEscape round-trips here, so this test proves nothing — check the decoder stand-in")
+	}
+	if strings.Contains(url.PathEscape(spoken), "+") {
+		t.Errorf("PathEscape(%q) still writes a plus", spoken)
+	}
+}