diff --git a/dlib/misc_api/misc_api_kernel_1.cpp b/dlib/misc_api/misc_api_kernel_1.cpp
index f17d850e1..a40d83e02 100644
--- a/dlib/misc_api/misc_api_kernel_1.cpp
+++ b/dlib/misc_api/misc_api_kernel_1.cpp
@@ -11,8 +11,8 @@
 #include "misc_api_kernel_1.h"
 
 #include "../windows_magic.h"
-#include <mmsystem.h>
 #include <windows.h>
+#include <mmsystem.h>
 
 // tell visual studio to link to the library needed to call timeGetTime() 
 #ifdef _MSC_VER
diff --git a/dlib/threads/threads_kernel_1.cpp b/dlib/threads/threads_kernel_1.cpp
index cb36b8d3f..178e9f5ac 100644
--- a/dlib/threads/threads_kernel_1.cpp
+++ b/dlib/threads/threads_kernel_1.cpp
@@ -9,11 +9,20 @@
 
 #include "threads_kernel_1.h"
 
+#include "../windows_magic.h"
+#include <windows.h>
+
 #include <process.h>
 
 
 namespace dlib
 {
+    thread_id_type get_thread_id(
+    )
+    {
+        return GetCurrentThreadId();
+    }
+
     namespace threads_kernel_shared_helpers
     {
 
diff --git a/dlib/threads/threads_kernel_1.h b/dlib/threads/threads_kernel_1.h
index 11acad5a5..426e6f023 100644
--- a/dlib/threads/threads_kernel_1.h
+++ b/dlib/threads/threads_kernel_1.h
@@ -9,8 +9,6 @@
 
 #include "threads_kernel_abstract.h"
 
-#include "../windows_magic.h"
-#include <windows.h>
 #include "../algs.h"
 #include <condition_variable>
 #include <mutex>
@@ -22,13 +20,9 @@ namespace dlib
 
 // ----------------------------------------------------------------------------------------
     
-    typedef DWORD thread_id_type;
+    typedef unsigned long thread_id_type;
 
-    inline thread_id_type get_thread_id (
-    )
-    {
-        return GetCurrentThreadId();
-    }
+    thread_id_type get_thread_id();
 
 // ----------------------------------------------------------------------------------------
 // ----------------------------------------------------------------------------------------