diff --git a/libc/utils/testutils/ExecuteFunctionUnix.cpp b/libc/utils/testutils/ExecuteFunctionUnix.cpp
--- a/libc/utils/testutils/ExecuteFunctionUnix.cpp
+++ b/libc/utils/testutils/ExecuteFunctionUnix.cpp
@@ -67,8 +67,10 @@
   }
 
   int WStatus = 0;
-  int status = ::waitpid(Pid, &WStatus, WNOHANG);
-  assert(status == Pid && "wait call should not block here");
+  pid_t status = ::waitpid(Pid, &WStatus, 0);
+  if (status == -1)
+    return ProcessStatus::Error("waitpid(2) failed");
+  assert(status == Pid);
   (void)status;
   return {WStatus};
 }