diff --git a/lang/cem/libcc.ansi/headers/setjmp.h b/lang/cem/libcc.ansi/headers/setjmp.h
index 804c91b3..b15673d8 100644
--- a/lang/cem/libcc.ansi/headers/setjmp.h
+++ b/lang/cem/libcc.ansi/headers/setjmp.h
@@ -1,5 +1,5 @@
 /*
- * setjmp.h - restore calling environment
+ * setjmp.h - save/restore calling environment
  *
  * (c) copyright 1987 by the Vrije Universiteit, Amsterdam, The Netherlands.
  * See the copyright notice in the ACK home directory, in the file "Copyright".
@@ -12,11 +12,18 @@
 /* In a jmp_buf, there is room for:  1 mask (long), 1 flag (int) and 3
  * pointers (stack-pointer, local base and program-counter). This may be
  * too big, but that doesn't matter. It could also be too small, when
- * sigset_t is larger than a long.
+ * sigset_t is larger than a long.  The fields is in the structure have no
+ * meaning, they just get the size right.
  * The identifier __setjmp has a special meaning to the compiler.
  */
 
-typedef char jmp_buf[ sizeof(long) + sizeof(int) + 3 * sizeof(void *)];
+typedef struct {
+	long __mask;
+	int __flag;
+	void (*__pc)();
+	void *__sp;
+	void *__lb;
+} jmp_buf[1];
 
 int	__setjmp(jmp_buf _env, int _savemask);