diff --git a/src/subprocess/cli.ts b/src/subprocess/cli.ts
index 1e76d82..5ba525a 100644
--- a/src/subprocess/cli.ts
+++ b/src/subprocess/cli.ts
@@ -14,7 +14,7 @@ interface Args {
   ['full-trace']?: boolean;
   require: string[];
   retries?: number;
-  slow?: boolean;
+  slow?: number;
   timeout?: number;
   test: string;
   file: string[];
@@ -59,7 +59,7 @@ const argv: Args = yargs
   .option('full-trace', {
     boolean: true,
   })
-  .boolean('slow')
+  .number('slow')
   .option('test', {
     demandOption: true,
     string: true,
diff --git a/src/thread.ts b/src/thread.ts
index 1225864..95daa2d 100644
--- a/src/thread.ts
+++ b/src/thread.ts
@@ -16,7 +16,7 @@ export interface ThreadOptions {
   file: string[];
   requires: string[];
   retries?: number;
-  slow?: boolean;
+  slow?: number;
   timeout?: number;
   ui?: string;
 }