diff --git a/lib/claude_code/adapter/port.ex b/lib/claude_code/adapter/port.ex
index 852d5f8..860a629 100644
--- a/lib/claude_code/adapter/port.ex
+++ b/lib/claude_code/adapter/port.ex
@@ -557,9 +557,14 @@ defmodule ClaudeCode.Adapter.Port do
 
   defp process_line("", state), do: state
 
+  # The CLI may emit non-map JSON values (booleans, arrays, numbers, strings) on
+  # stdout when, for example, a hook callback fails and a Zod schema validation
+  # error is printed alongside the normal stream-JSON output. Filter those out
+  # here so they never reach `Control.classify/1` (which is spec'd to take a map)
+  # or `handle_sdk_message/2` (whose clauses index with `json["type"]`).
   defp process_line(line, state) do
     case Jason.decode(line) do
-      {:ok, json} ->
+      {:ok, json} when is_map(json) ->
         case Control.classify(json) do
           {:control_response, msg} ->
             handle_control_response(msg, state)
@@ -574,6 +579,10 @@ defmodule ClaudeCode.Adapter.Port do
             handle_sdk_message(json_msg, state)
         end
 
+      {:ok, non_map} ->
+        Logger.warning("Dropping non-map CLI output: #{inspect(non_map)}")
+        state
+
       {:error, _} ->
         Logger.debug("Non-JSON CLI output: #{String.slice(line, 0, 500)}")
         state
diff --git a/test/claude_code/adapter/port_integration_test.exs b/test/claude_code/adapter/port_integration_test.exs
index 2e31ed8..43e18f5 100644
--- a/test/claude_code/adapter/port_integration_test.exs
+++ b/test/claude_code/adapter/port_integration_test.exs
@@ -54,6 +54,49 @@ defmodule ClaudeCode.Adapter.PortIntegrationTest do
     end
   end
 
+  describe "non-map JSON in stream" do
+    setup do
+      # CLI emits a non-map JSON line (`true`) between a normal system message
+      # and the final result. Without the `when not is_map(json)` guard in
+      # `handle_sdk_message/2`, the Port GenServer would crash with a
+      # `FunctionClauseError` from `Access.get(true, "type", nil)` and abort the
+      # in-flight session.
+      MockCLI.setup_with_script("""
+      #!/bin/bash
+      while IFS= read -r line; do
+        if echo "$line" | grep -q '"type":"control_request"'; then
+          REQ_ID=$(echo "$line" | grep -o '"request_id":"[^"]*"' | cut -d'"' -f4)
+          echo "{\\\"type\\\":\\\"control_response\\\",\\\"response\\\":{\\\"subtype\\\":\\\"success\\\",\\\"request_id\\\":\\\"$REQ_ID\\\",\\\"response\\\":{}}}"
+        else
+          echo '{"type":"system","subtype":"init","cwd":"/test","session_id":"nonmap-test","tools":[],"mcp_servers":[],"model":"claude-3","permissionMode":"auto","apiKeySource":"ANTHROPIC_API_KEY"}'
+          echo 'true'
+          echo '[1,2,3]'
+          echo '42'
+          echo '{"type":"result","subtype":"success","is_error":false,"duration_ms":50,"duration_api_ms":40,"num_turns":1,"result":"survived","session_id":"nonmap-test","total_cost_usd":0.001,"usage":{}}'
+        fi
+      done
+      exit 0
+      """)
+    end
+
+    test "session survives and returns a result when CLI emits non-map JSON", %{
+      mock_script: mock_script
+    } do
+      {:ok, session} = ClaudeCode.start_link(api_key: "test-key", cli_path: mock_script)
+
+      messages =
+        session
+        |> ClaudeCode.stream("hello")
+        |> Enum.to_list()
+
+      result = Enum.find(messages, &match?(%ResultMessage{}, &1))
+      assert result != nil
+      assert result.result == "survived"
+
+      GenServer.stop(session)
+    end
+  end
+
   describe "stream completed normally" do
     setup do
       MockCLI.setup_with_script("""
diff --git a/test/claude_code/adapter/port_test.exs b/test/claude_code/adapter/port_test.exs
index 434ea76..6b28c15 100644
--- a/test/claude_code/adapter/port_test.exs
+++ b/test/claude_code/adapter/port_test.exs
@@ -1741,7 +1741,7 @@ defmodule ClaudeCode.Adapter.PortTest do
           Port.filter_system_env(%{"PATH" => "/usr/bin"}, ["NONEXISTENT_VAR"])
         end)
 
-      assert log == ""
+      refute log =~ "no matching system env"
     end
 
     test "no logging for :all mode even with debug" do
@@ -1750,7 +1750,7 @@ defmodule ClaudeCode.Adapter.PortTest do
           Port.filter_system_env(%{"PATH" => "/usr/bin"}, :all, debug: true)
         end)
 
-      assert log == ""
+      refute log =~ "no matching system env"
     end
   end
 end