diff --git a/cli.py b/cli.py
index abd4d2391..38701bd1a 100644
--- a/cli.py
+++ b/cli.py
@@ -7808,10 +7808,14 @@ class HermesCLI:
         try:
             from hermes_cli.config import load_config
             _raw_ptt = load_config().get("voice", {}).get("record_key", "ctrl+b")
-            _ptt_key = _raw_ptt.lower().replace("ctrl+", "c-").replace("alt+", "a-")
+            _raw_ptt_lower = _raw_ptt.lower()
+            if "alt+" in _raw_ptt_lower:
+                _ptt_key = "c-b"
+            else:
+                _ptt_key = _raw_ptt_lower.replace("ctrl+", "c-").replace("shift+", "s-")
         except Exception:
             _ptt_key = "c-b"
-        _ptt_display = _ptt_key.replace("c-", "Ctrl+").upper()
+        _ptt_display = _ptt_key.replace("c-", "Ctrl+").replace("s-", "Shift+").upper()
         _cprint(f"\n{_ACCENT}Voice mode enabled{tts_status}{_RST}")
         _cprint(f"  {_DIM}{_ptt_display} to start/stop recording{_RST}")
         _cprint(f"  {_DIM}/voice tts  to toggle speech output{_RST}")
@@ -9611,7 +9615,13 @@ class HermesCLI:
         try:
             from hermes_cli.config import load_config
             _raw_key = load_config().get("voice", {}).get("record_key", "ctrl+b")
-            _voice_key = _raw_key.lower().replace("ctrl+", "c-").replace("alt+", "a-")
+            _raw_lower = _raw_key.lower()
+            if "alt+" in _raw_lower:
+                import sys as _sys
+                print(f"[hermes] voice.record_key '{_raw_key}': alt+ modifier not supported by prompt_toolkit, falling back to ctrl+b", file=_sys.stderr)
+                _voice_key = "c-b"
+            else:
+                _voice_key = _raw_lower.replace("ctrl+", "c-").replace("shift+", "s-")
         except Exception:
             _voice_key = "c-b"
 
diff --git a/tests/hermes_cli/test_voice_record_key.py b/tests/hermes_cli/test_voice_record_key.py
new file mode 100644
index 000000000..c0cd47ac4
--- /dev/null
+++ b/tests/hermes_cli/test_voice_record_key.py
@@ -0,0 +1,41 @@
+"""Regression tests for voice.record_key alt+ modifier handling (#11387).
+
+Setting voice.record_key to alt+<key> in config.yaml crashed startup because
+prompt_toolkit only accepts c- (Ctrl) and s- (Shift) prefixes, not a- (Alt).
+"""
+import pytest
+from unittest.mock import patch, MagicMock
+
+
+def _translate_voice_key(raw_key: str) -> str:
+    """Mirrors the key-translation logic in cli.py (keybinding setup ~L8853)."""
+    raw_lower = raw_key.lower()
+    if "alt+" in raw_lower:
+        return "c-b"
+    return raw_lower.replace("ctrl+", "c-").replace("shift+", "s-")
+
+
+class TestVoiceRecordKeyTranslation:
+    """Unit tests for the record_key → prompt_toolkit key translation."""
+
+    def test_ctrl_b_default(self):
+        assert _translate_voice_key("ctrl+b") == "c-b"
+
+    def test_ctrl_t(self):
+        assert _translate_voice_key("ctrl+t") == "c-t"
+
+    def test_shift_f1(self):
+        assert _translate_voice_key("shift+f1") == "s-f1"
+
+    def test_alt_space_falls_back(self):
+        """alt+ modifier is unsupported; must fall back to c-b (#11387)."""
+        assert _translate_voice_key("alt+space") == "c-b"
+
+    def test_alt_x_falls_back(self):
+        assert _translate_voice_key("alt+x") == "c-b"
+
+    def test_alt_mixed_case_falls_back(self):
+        assert _translate_voice_key("Alt+Space") == "c-b"
+
+    def test_ctrl_uppercase(self):
+        assert _translate_voice_key("CTRL+B") == "c-b"