diff --git a/lldb/packages/Python/lldbsuite/test/tools/lldb-server/gdbremote_testcase.py b/lldb/packages/Python/lldbsuite/test/tools/lldb-server/gdbremote_testcase.py
index 19c766996292e..aea6b9fe36b2c 100644
--- a/lldb/packages/Python/lldbsuite/test/tools/lldb-server/gdbremote_testcase.py
+++ b/lldb/packages/Python/lldbsuite/test/tools/lldb-server/gdbremote_testcase.py
@@ -444,13 +444,20 @@ def launch_process_for_attach(
         if not exe_path:
             exe_path = self.getBuildArtifact("a.out")
 
-        args = []
+        # This file will be created once the inferior has enabled attaching.
+        sync_file_path = lldbutil.append_to_process_working_directory(
+            self, "process_ready"
+        )
+        args = [f"syncfile:{sync_file_path}"]
         if inferior_args:
             args.extend(inferior_args)
         if sleep_seconds:
             args.append("sleep:%d" % sleep_seconds)
 
-        return self.spawnSubprocess(exe_path, args)
+        inferior = self.spawnSubprocess(exe_path, args)
+        lldbutil.wait_for_file_on_target(self, sync_file_path)
+
+        return inferior
 
     def prep_debug_monitor_and_inferior(
         self,
diff --git a/lldb/test/API/tools/lldb-server/main.cpp b/lldb/test/API/tools/lldb-server/main.cpp
index 0e9323cce88cf..7e84552b0f25d 100644
--- a/lldb/test/API/tools/lldb-server/main.cpp
+++ b/lldb/test/API/tools/lldb-server/main.cpp
@@ -5,6 +5,7 @@
 #include <cstdlib>
 #include <cstring>
 #include <errno.h>
+#include <fstream>
 #include <future>
 #include <inttypes.h>
 #include <memory>
@@ -265,7 +266,11 @@ int main(int argc, char **argv) {
   // Process command line args.
   for (int i = 1; i < argc; ++i) {
     std::string arg = argv[i];
-    if (consume_front(arg, "stderr:")) {
+    if (consume_front(arg, "syncfile:")) {
+      // Write to this file to tell test framework that attaching is now
+      // possible.
+      std::ofstream(arg).close();
+    } else if (consume_front(arg, "stderr:")) {
       // Treat remainder as text to go to stderr.
       fprintf(stderr, "%s\n", arg.c_str());
     } else if (consume_front(arg, "retval:")) {