diff --git a/Include/osdefs.h b/Include/osdefs.h
index 3243944a148..2599e87a9d7 100644
--- a/Include/osdefs.h
+++ b/Include/osdefs.h
@@ -1,51 +1,57 @@
+// Operating system dependencies.
+//
+// Define constants:
+//
+// - ALTSEP
+// - DELIM
+// - MAXPATHLEN
+// - SEP
+
 #ifndef Py_OSDEFS_H
 #define Py_OSDEFS_H
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-
-/* Operating system dependencies */
-
 #ifdef MS_WINDOWS
-#define SEP L'\\'
-#define ALTSEP L'/'
-#define MAXPATHLEN 256
-#define DELIM L';'
+#  define SEP L'\\'
+#  define ALTSEP L'/'
+#  define MAXPATHLEN 256
+#  define DELIM L';'
 #endif
 
 #ifdef __VXWORKS__
-#define DELIM L';'
+#  define DELIM L';'
 #endif
 
 /* Filename separator */
 #ifndef SEP
-#define SEP L'/'
+#  define SEP L'/'
 #endif
 
 /* Max pathname length */
 #ifdef __hpux
-#include <sys/param.h>
-#include <limits.h>
-#ifndef PATH_MAX
-#define PATH_MAX MAXPATHLEN
-#endif
+#  include <sys/param.h>
+#  include <limits.h>
+#  ifndef PATH_MAX
+#    define PATH_MAX MAXPATHLEN
+#  endif
 #endif
 
 #ifndef MAXPATHLEN
-#if defined(PATH_MAX) && PATH_MAX > 1024
-#define MAXPATHLEN PATH_MAX
-#else
-#define MAXPATHLEN 1024
-#endif
+#  if defined(PATH_MAX) && PATH_MAX > 1024
+#    define MAXPATHLEN PATH_MAX
+#  else
+#    define MAXPATHLEN 1024
+#  endif
 #endif
 
 /* Search path entry delimiter */
 #ifndef DELIM
-#define DELIM L':'
+#  define DELIM L':'
 #endif
 
 #ifdef __cplusplus
 }
 #endif
-#endif /* !Py_OSDEFS_H */
+#endif   // !Py_OSDEFS_H