diff --git a/compat/obstack.c b/compat/obstack.c
index 4d1d95beeb..27cd5c1ea1 100644
--- a/compat/obstack.c
+++ b/compat/obstack.c
@@ -112,15 +112,15 @@ compat_symbol (libc, _obstack_compat, _obstack, GLIBC_2_0);
 
 # define CALL_CHUNKFUN(h, size) \
   (((h) -> use_extra_arg) \
-   ? (*(h)->chunkfun) ((h)->extra_arg, (size)) \
-   : (*(struct _obstack_chunk *(*) (long)) (h)->chunkfun) ((size)))
+   ? (*(h)->chunkfun.extra) ((h)->extra_arg, (size)) \
+   : (*(h)->chunkfun.plain) ((size)))
 
 # define CALL_FREEFUN(h, old_chunk) \
   do { \
     if ((h) -> use_extra_arg) \
-      (*(h)->freefun) ((h)->extra_arg, (old_chunk)); \
+      (*(h)->freefun.extra) ((h)->extra_arg, (old_chunk)); \
     else \
-      (*(void (*) (void *)) (h)->freefun) ((old_chunk)); \
+      (*(h)->freefun.plain) ((old_chunk)); \
   } while (0)
 
 
@@ -159,8 +159,8 @@ _obstack_begin (struct obstack *h,
       size = 4096 - extra;
     }
 
-  h->chunkfun = (struct _obstack_chunk * (*)(void *, long)) chunkfun;
-  h->freefun = (void (*) (void *, struct _obstack_chunk *)) freefun;
+  h->chunkfun.plain = chunkfun;
+  h->freefun.plain = freefun;
   h->chunk_size = size;
   h->alignment_mask = alignment - 1;
   h->use_extra_arg = 0;
@@ -206,8 +206,9 @@ _obstack_begin_1 (struct obstack *h, int size, int alignment,
       size = 4096 - extra;
     }
 
-  h->chunkfun = (struct _obstack_chunk * (*)(void *,long)) chunkfun;
-  h->freefun = (void (*) (void *, struct _obstack_chunk *)) freefun;
+  h->chunkfun.extra = (struct _obstack_chunk * (*)(void *,long)) chunkfun;
+  h->freefun.extra = (void (*) (void *, struct _obstack_chunk *)) freefun;
+
   h->chunk_size = size;
   h->alignment_mask = alignment - 1;
   h->extra_arg = arg;
diff --git a/compat/obstack.h b/compat/obstack.h
index 6bc24b7644..ced94d0118 100644
--- a/compat/obstack.h
+++ b/compat/obstack.h
@@ -160,11 +160,15 @@ struct obstack		/* control current object in current chunk */
     void *tempptr;
   } temp;			/* Temporary for some macros.  */
   int   alignment_mask;		/* Mask of alignment for each object. */
-  /* These prototypes vary based on `use_extra_arg', and we use
-     casts to the prototypeless function type in all assignments,
-     but having prototypes here quiets -Wstrict-prototypes.  */
-  struct _obstack_chunk *(*chunkfun) (void *, long);
-  void (*freefun) (void *, struct _obstack_chunk *);
+  /* These prototypes vary based on `use_extra_arg'. */
+  union {
+    void *(*plain) (long);
+    struct _obstack_chunk *(*extra) (void *, long);
+  } chunkfun;
+  union {
+    void (*plain) (void *);
+    void (*extra) (void *, struct _obstack_chunk *);
+  } freefun;
   void *extra_arg;		/* first arg for chunk alloc/dealloc funcs */
   unsigned use_extra_arg:1;	/* chunk alloc/dealloc funcs take extra arg */
   unsigned maybe_empty_object:1;/* There is a possibility that the current
@@ -235,10 +239,10 @@ extern void (*obstack_alloc_failed_handler) (void);
 		    (void (*) (void *, void *)) (freefun), (arg))
 
 #define obstack_chunkfun(h, newchunkfun) \
-  ((h) -> chunkfun = (struct _obstack_chunk *(*)(void *, long)) (newchunkfun))
+  ((h)->chunkfun.extra = (struct _obstack_chunk *(*)(void *, long)) (newchunkfun))
 
 #define obstack_freefun(h, newfreefun) \
-  ((h) -> freefun = (void (*)(void *, struct _obstack_chunk *)) (newfreefun))
+  ((h)->freefun.extra = (void (*)(void *, struct _obstack_chunk *)) (newfreefun))
 
 #define obstack_1grow_fast(h,achar) (*((h)->next_free)++ = (achar))