diff --git a/src/cli/CLICommand.ts b/src/cli/CLICommand.ts
index 3d59e90f..1ee9e5c5 100644
--- a/src/cli/CLICommand.ts
+++ b/src/cli/CLICommand.ts
@@ -1,3 +1,4 @@
+import * as child_process from 'node:child_process';
 
 export interface CLICommand {
 
@@ -7,3 +8,15 @@ export interface CLICommand {
   run(argv: string[]): Promise<any>;
 
 }
+
+export function processSpawnResult(result : child_process.SpawnSyncReturns<Buffer>) {
+  if (result.error !== undefined) {
+    throw result.error;
+  }
+  if (result.signal !== null) {
+    throw Error(`Child process has been killed by signal ${result.signal}`);
+  }
+  if (result.status !== null && result.status !== 0) {
+    throw Error(`Child process exited with non-zero status ${result.status}`);
+  }
+}
diff --git a/src/cli/OutputGTFSZipCommand.ts b/src/cli/OutputGTFSZipCommand.ts
index b1acd20a..fad777f9 100644
--- a/src/cli/OutputGTFSZipCommand.ts
+++ b/src/cli/OutputGTFSZipCommand.ts
@@ -1,10 +1,10 @@
 
 import * as os from 'node:os';
 import * as path from 'node:path';
-import {CLICommand} from "./CLICommand";
+import {CLICommand, processSpawnResult} from "./CLICommand";
 import {OutputGTFSCommand} from "./OutputGTFSCommand";
 import * as fs from "fs";
-import {execSync} from "child_process";
+import {spawnSync} from "child_process";
 
 export class OutputGTFSZipCommand implements CLICommand {
 
@@ -29,8 +29,8 @@ export class OutputGTFSZipCommand implements CLICommand {
     // when node tells you it's finished writing a file, it's lying.
     setTimeout(() => {
       console.log("Writing " + filename);
-      execSync(`zip -j ${filename} ${argv[3]}/*.txt`);
+      processSpawnResult(spawnSync('zip', ['-jr', filename, argv[3]]));
     }, 1000);
   }
 
-}
\ No newline at end of file
+}