diff --git a/lib/libc/arch/i386/sys-minix/Makefile.inc b/lib/libc/arch/i386/sys-minix/Makefile.inc
index 82b6ee2ed..0c933edca 100644
--- a/lib/libc/arch/i386/sys-minix/Makefile.inc
+++ b/lib/libc/arch/i386/sys-minix/Makefile.inc
@@ -1,5 +1,15 @@
 # rts sources
-.PATH: ${.CURDIR}/arch/${MACHINE_ARCH}/sys-minix
+HERE=${.CURDIR}/arch/${MACHINE_ARCH}/sys-minix
+.PATH: ${HERE}
+
+TMP=ucontextoffsets.h.tmp
+INCLS=../../include
+ARCHINCLS=$(INCLS)/arch/i386/include/
+CF=ucontextoffsets.cf
+
+INCS+=ucontextoffsets.h
+
+ucontext.d: ucontextoffsets.h
 
 SRCS+=   \
 	__sigreturn.S \
@@ -7,3 +17,10 @@ SRCS+=   \
 	_senda.S \
 	brksize.S \
 	ucontext.S
+
+ucontextoffsets.h: $(CF) $(ARCHINCLS)/stackframe.h $(INCLS)/sys/ucontext.h
+	${_MKTARGET_CREATE}
+	cat ${HERE}/$(CF) | \
+		${TOOL_GENASSYM} -- ${CC} ${CFLAGS} ${CPPFLAGS} ${PROF} >$TMP && \
+	mv -f $TMP $@
+
diff --git a/lib/libc/arch/i386/sys-minix/ucontext.S b/lib/libc/arch/i386/sys-minix/ucontext.S
index 27e237e36..3c73c0970 100644
--- a/lib/libc/arch/i386/sys-minix/ucontext.S
+++ b/lib/libc/arch/i386/sys-minix/ucontext.S
@@ -1,4 +1,5 @@
 #include <machine/asm.h>
+#include <ucontextoffsets.h>
 
 #ifdef __ACK__
 .text
@@ -21,31 +22,6 @@ IMPORT(setuctx)
 IMPORT(resumecontext)
 
 
-/* Offsets into ucontext_t structure. Keep in sync with <sys/ucontext.h>! */
-#define UC_FLAGS	0 
-#define UC_LINK		UC_FLAGS + 4
-#define MCTX		UC_LINK + 4
-#define MAGIC		MCTX
-#define GS		MAGIC+4
-#define FS		GS+2
-#define ES		FS+2
-#define DS		ES+2
-#define DI		DS+2
-#define SI		DI+4
-#define BP		SI+4
-#define ST		BP+4	/* Hole for another SP */
-#define BX		ST+4
-#define DX		BX+4
-#define CX		DX+4
-#define AX		CX+4
-#define RETADR		AX+4
-#define PC		RETADR+4
-#define CS		PC+4
-#define PSW		CS+4
-#define SP		PSW+4
-#define SS		SP+4
-
-
 /* MCF_MAGIC value from <mcontext.h> */
 #define MCF_MAGIC	0xc0ffee
 
diff --git a/lib/libc/arch/i386/sys-minix/ucontextoffsets.cf b/lib/libc/arch/i386/sys-minix/ucontextoffsets.cf
new file mode 100644
index 000000000..6473f569a
--- /dev/null
+++ b/lib/libc/arch/i386/sys-minix/ucontextoffsets.cf
@@ -0,0 +1,18 @@
+
+include <minix/type.h>
+include <sys/ucontext.h>
+
+struct __ucontext
+member UC_FLAGS uc_flags
+member UC_LINK uc_link
+member MAGIC uc_mcontext.mc_magic
+member DI uc_mcontext.mc_p_reg.di
+member SI uc_mcontext.mc_p_reg.si
+member BP uc_mcontext.mc_p_reg.fp
+member AX uc_mcontext.mc_p_reg.retreg
+member BX uc_mcontext.mc_p_reg.bx
+member CX uc_mcontext.mc_p_reg.cx
+member DX uc_mcontext.mc_p_reg.dx
+member PC uc_mcontext.mc_p_reg.pc
+member SP uc_mcontext.mc_p_reg.sp
+