diff --git a/compat/err.c b/compat/err.c
index aab93b5..dd07cf9 100644
--- a/compat/err.c
+++ b/compat/err.c
@@ -18,9 +18,7 @@
 #include <stdio.h>
 #include <stdarg.h>
 
-/* cheat: if we don't have getprogname in libc, we will link against
- * compat/getprogname.c anyway. */
-const char *getprogname(void);
+#include "../config.h"
 
 static void vwarn_impl(const char*, va_list);
 static void vwarnx_impl(const char*, va_list);
diff --git a/compat/explicit_bzero.c b/compat/explicit_bzero.c
index 674b8e2..f502b4b 100644
--- a/compat/explicit_bzero.c
+++ b/compat/explicit_bzero.c
@@ -5,6 +5,8 @@
 
 #include <string.h>
 
+#include "../config.h"
+
 void
 explicit_bzero(void *buf, size_t len)
 {
diff --git a/compat/getprogname.c b/compat/getprogname.c
index f162268..ee178b7 100644
--- a/compat/getprogname.c
+++ b/compat/getprogname.c
@@ -14,6 +14,8 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+#include "../config.h"
+
 const char *
 getprogname(void)
 {
diff --git a/compat/recallocarray.c b/compat/recallocarray.c
index 1baffbb..70ad582 100644
--- a/compat/recallocarray.c
+++ b/compat/recallocarray.c
@@ -20,6 +20,8 @@
 #include <string.h>
 #include <unistd.h>
 
+#include "../config.h"
+
 /*
  * This is sqrt(SIZE_MAX+1), as s1*s2 <= SIZE_MAX
  * if both s1 < MUL_NO_OVERFLOW and s2 < MUL_NO_OVERFLOW
@@ -34,10 +36,6 @@
  */
 #define getpagesize()	(1UL << 12)
 
-/* cheat: provide a prototype for explicit_bzero: if libc doesn't
- * provide it, we will link to compat/explicit_bzero.c anyway. */
-void explicit_bzero(void*, size_t);
-
 void *
 recallocarray(void *ptr, size_t oldnmemb, size_t newnmemb, size_t size)
 {
diff --git a/compat/strlcat.c b/compat/strlcat.c
index 1c19062..b4e969e 100644
--- a/compat/strlcat.c
+++ b/compat/strlcat.c
@@ -17,6 +17,8 @@
 #include <sys/types.h>
 #include <string.h>
 
+#include "../config.h"
+
 /*
  * Appends src to string dst of size dsize (unlike strncat, dsize is the
  * full size of dst, not space left).  At most dsize-1 characters
diff --git a/compat/strlcpy.c b/compat/strlcpy.c
index 177ff72..75636a0 100644
--- a/compat/strlcpy.c
+++ b/compat/strlcpy.c
@@ -17,6 +17,8 @@
 #include <sys/types.h>
 #include <string.h>
 
+#include "../config.h"
+
 /*
  * Copy string src to buffer dst of size dsize.  At most dsize-1
  * chars will be copied.  Always NUL terminates (unless dsize == 0).
diff --git a/compat/strtonum.c b/compat/strtonum.c
index 6e6cb76..09c4fbe 100644
--- a/compat/strtonum.c
+++ b/compat/strtonum.c
@@ -14,12 +14,13 @@
  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
-#include "config.h"
 
 #include <errno.h>
 #include <limits.h>
 #include <stdlib.h>
 
+#include "../config.h"
+
 #define	INVALID		1
 #define	TOOSMALL	2
 #define	TOOLARGE	3
diff --git a/compat/vasprintf.c b/compat/vasprintf.c
index d76f3ef..69586f0 100644
--- a/compat/vasprintf.c
+++ b/compat/vasprintf.c
@@ -25,6 +25,8 @@
 #include <stdio.h>
 #include <stdlib.h>
 
+#include "../config.h"
+
 int
 vasprintf(char **ret, const char *format, va_list ap)
 {
diff --git a/configure b/configure
index 97c5dd8..359143f 100755
--- a/configure
+++ b/configure
@@ -272,6 +272,14 @@ cat <<__HEREDOC__
 
 __HEREDOC__
 
+[ ${HAVE_VASPRINTF} -eq 0 ] && echo "#include <stdarg.h>"
+
+[ ${HAVE_EXPLICIT_BZERO} -eq 0 -o \
+  ${HAVE_RECALLOCARRAY} -eq 0 -o \
+  ${HAVE_STRLCAT} -eq 0 -o \
+  ${HAVE_STRLCPY} -eq 0 -o \
+  ${HAVE_STRTONUM} -eq 0 ] && echo "#include <stddef.h>"
+
 if [ ${HAVE_ERR} -eq 0 ]; then
 	echo "extern	void	 err(int, const char*, ...);"
 	echo "extern	void	 errx(int, const char*, ...);"