diff --git a/backend/src/server.py b/backend/src/server.py
index 1368c91..d871a76 100644
--- a/backend/src/server.py
+++ b/backend/src/server.py
@@ -17,6 +17,7 @@ CONTENT_TYPES = {
 }
 
 app = FastAPI(title="whisper-remote-backend")
+WHISPER_PROCESS_TIMEOUT_SECONDS = 300
 
 
 def validate_output_format(output_format: str) -> str:
@@ -112,12 +113,21 @@ async def transcribe(
                 check=False,
                 capture_output=True,
                 text=True,
+                timeout=WHISPER_PROCESS_TIMEOUT_SECONDS,
             )
         except FileNotFoundError as exc:
             raise HTTPException(
                 status_code=500,
                 detail="The 'whisper' CLI was not found on PATH on the backend host.",
             ) from exc
+        except subprocess.TimeoutExpired as exc:
+            raise HTTPException(
+                status_code=504,
+                detail=(
+                    "Whisper CLI timed out after "
+                    f"{WHISPER_PROCESS_TIMEOUT_SECONDS}s and was terminated."
+                ),
+            ) from exc
 
         if completed.returncode != 0:
             detail = completed.stderr.strip() or completed.stdout.strip() or "Whisper CLI failed."
diff --git a/backend/tests/test_server.py b/backend/tests/test_server.py
index 59baf5d..1e95638 100644
--- a/backend/tests/test_server.py
+++ b/backend/tests/test_server.py
@@ -64,3 +64,22 @@ def test_transcriptions_maps_subprocess_failure(monkeypatch) -> None:
 
     assert response.status_code == 502
     assert response.json()["detail"] == "bad whisper day"
+
+
+def test_transcriptions_maps_subprocess_timeout(monkeypatch) -> None:
+    def fake_run(command: list[str], check: bool, capture_output: bool, text: bool, timeout: int):
+        raise server.subprocess.TimeoutExpired(cmd=command, timeout=timeout)
+
+    monkeypatch.setattr(server.subprocess, "run", fake_run)
+
+    response = client.post(
+        "/transcriptions",
+        data={"model": "base", "output_format": "txt"},
+        files={"file": ("clip.wav", b"audio", "audio/wav")},
+    )
+
+    assert response.status_code == 504
+    assert (
+        response.json()["detail"]
+        == f"Whisper CLI timed out after {server.WHISPER_PROCESS_TIMEOUT_SECONDS}s and was terminated."
+    )
diff --git a/cli/src/main.py b/cli/src/main.py
index 5ddbe54..ae533db 100644
--- a/cli/src/main.py
+++ b/cli/src/main.py
@@ -64,6 +64,14 @@ def format_http_error(response: httpx.Response, endpoint: str) -> str:
     return f"HTTP {response.status_code} from {endpoint}: {body}"
 
 
+def format_request_error(exc: httpx.RequestError, endpoint: str) -> str:
+    if isinstance(exc, httpx.TimeoutException):
+        return f"Request to {endpoint} timed out."
+
+    reason = str(exc).strip() or exc.__class__.__name__
+    return f"Request to {endpoint} failed: {reason}"
+
+
 def main() -> int:
     parser = build_parser()
     args = parser.parse_args()
@@ -75,16 +83,19 @@ def main() -> int:
     server = resolve_server(args)
     endpoint = f"{server}/transcriptions"
 
-    with input_file.open("rb") as handle, httpx.Client(timeout=300.0) as client:
-        response = client.post(
-            endpoint,
-            data={
-                "model": args.model,
-                "language": args.language or "",
-                "output_format": args.output_format,
-            },
-            files={"file": (input_file.name, handle, "application/octet-stream")},
-        )
+    try:
+        with input_file.open("rb") as handle, httpx.Client(timeout=300.0) as client:
+            response = client.post(
+                endpoint,
+                data={
+                    "model": args.model,
+                    "language": args.language or "",
+                    "output_format": args.output_format,
+                },
+                files={"file": (input_file.name, handle, "application/octet-stream")},
+            )
+    except httpx.RequestError as exc:
+        parser.exit(1, f"{format_request_error(exc, endpoint)}\n")
 
     try:
         response.raise_for_status()
diff --git a/cli/tests/test_main.py b/cli/tests/test_main.py
index b1c4c1e..42fca89 100644
--- a/cli/tests/test_main.py
+++ b/cli/tests/test_main.py
@@ -44,3 +44,20 @@ def test_format_http_error_with_empty_body() -> None:
     response = httpx.Response(500, text="", request=request)
     message = main.format_http_error(response, "http://localhost:8000/transcriptions")
     assert message == "HTTP 500 from http://localhost:8000/transcriptions: <empty response body>"
+
+
+def test_format_request_error_timeout() -> None:
+    request = httpx.Request("POST", "http://localhost:8000/transcriptions")
+    exc = httpx.ReadTimeout("read timed out", request=request)
+    message = main.format_request_error(exc, "http://localhost:8000/transcriptions")
+    assert message == "Request to http://localhost:8000/transcriptions timed out."
+
+
+def test_format_request_error_network_failure() -> None:
+    request = httpx.Request("POST", "http://localhost:8000/transcriptions")
+    exc = httpx.ConnectError("connection refused", request=request)
+    message = main.format_request_error(exc, "http://localhost:8000/transcriptions")
+    assert (
+        message
+        == "Request to http://localhost:8000/transcriptions failed: connection refused"
+    )