diff --git a/rtc_base/platform_thread.h b/rtc_base/platform_thread.h
index 2c82c02455..3ab2761f43 100644
--- a/rtc_base/platform_thread.h
+++ b/rtc_base/platform_thread.h
@@ -55,6 +55,10 @@ class PlatformThread final {
   // removed.
   PlatformThread(PlatformThread&& rhs);
 
+  // Copies won't work since we'd have problems with joinable threads.
+  PlatformThread(const PlatformThread&) = delete;
+  PlatformThread& operator=(const PlatformThread&) = delete;
+
   // Moves `rhs` into this, storing an empty state in `rhs`.
   // TODO(bugs.webrtc.org/12727) Look into if default and move support can be
   // removed.