diff --git a/src/claude_agent_sdk/client.py b/src/claude_agent_sdk/client.py
index c6ad1171..93cbb77b 100644
--- a/src/claude_agent_sdk/client.py
+++ b/src/claude_agent_sdk/client.py
@@ -1,6 +1,7 @@
 """Claude SDK Client for interacting with Claude Code."""
 
 import json
+import math
 import os
 from collections.abc import AsyncIterable, AsyncIterator
 from dataclasses import asdict, replace
@@ -20,6 +21,29 @@
 )
 
 
+def _parse_timeout_ms_from_env(
+    env_var: str, default_timeout_ms: float = 60000.0
+) -> float:
+    """Parse timeout milliseconds from environment, falling back safely.
+
+    Accepts integer or float-like strings. Invalid or non-finite values return
+    the provided default.
+    """
+    raw = os.environ.get(env_var)
+    if raw is None:
+        return default_timeout_ms
+
+    try:
+        parsed = float(raw)
+    except (TypeError, ValueError):
+        return default_timeout_ms
+
+    if not math.isfinite(parsed):
+        return default_timeout_ms
+
+    return parsed
+
+
 class ClaudeSDKClient:
     """
     Client for bidirectional, interactive conversations with Claude Code.
@@ -152,8 +176,8 @@ async def _empty_stream() -> AsyncIterator[dict[str, Any]]:
 
         # Calculate initialize timeout from CLAUDE_CODE_STREAM_CLOSE_TIMEOUT env var if set
         # CLAUDE_CODE_STREAM_CLOSE_TIMEOUT is in milliseconds, convert to seconds
-        initialize_timeout_ms = int(
-            os.environ.get("CLAUDE_CODE_STREAM_CLOSE_TIMEOUT", "60000")
+        initialize_timeout_ms = _parse_timeout_ms_from_env(
+            "CLAUDE_CODE_STREAM_CLOSE_TIMEOUT"
         )
         initialize_timeout = max(initialize_timeout_ms / 1000.0, 60.0)
 
diff --git a/tests/test_streaming_client.py b/tests/test_streaming_client.py
index 1c2b6980..a786247e 100644
--- a/tests/test_streaming_client.py
+++ b/tests/test_streaming_client.py
@@ -2,6 +2,7 @@
 
 import asyncio
 import json
+import os
 import sys
 import tempfile
 from pathlib import Path
@@ -1203,6 +1204,34 @@ async def _test():
 
         anyio.run(_test)
 
+    def test_connect_with_invalid_timeout_env_falls_back_to_default(self):
+        """Malformed timeout env values should not break connect()."""
+
+        async def _test():
+            with (
+                patch.dict(
+                    os.environ,
+                    {"CLAUDE_CODE_STREAM_CLOSE_TIMEOUT": "60s"},
+                    clear=False,
+                ),
+                patch(
+                    "claude_agent_sdk._internal.transport.subprocess_cli.SubprocessCLITransport"
+                ) as mock_transport_class,
+            ):
+                mock_transport = create_mock_transport()
+                mock_transport_class.return_value = mock_transport
+
+                client = ClaudeSDKClient()
+                await client.connect()
+
+                assert client._query is not None
+                # Default is 60000ms, and initialize timeout enforces a 60s minimum.
+                assert client._query._initialize_timeout == 60.0
+
+                await client.disconnect()
+
+        anyio.run(_test)
+
     def test_disconnect_without_connect(self):
         """Test disconnecting without connecting first."""