diff --git a/ent.c b/ent.c
index fee4cd674..70e595a19 100644
--- a/ent.c
+++ b/ent.c
@@ -1,59 +1,58 @@
 #include <ent/config.h>
 
-/* ent.h undefs these constants and config.h is #pragma once. */
+/* ent.h undefs all constants and config.h is #pragma once. */
 
 #if defined(ENT_GETRANDOM)
-#define _ENT_GETRANDOM
+
+#define _ENT_IMPL
 #define _GNU_SOURCE
-#endif
-
-#if defined(ENT_URANDOM)
-#define _ENT_URANDOM
-#endif
-
-#include <ent/ent.h>
-
-#if defined(_ENT_GETRANDOM) || defined(_ENT_URANDOM)
-
-#include <assert.h>
-#include <errno.h>
 #include <unistd.h>
-
-#if defined(_ENT_GETRANDOM)
-
 #include <sys/syscall.h>
 
-#elif defined(_ENT_URANDOM)
+#define ENT_DEFS (void)0
+#define ENT_INIT() (void)0
+#define ENT_READ(B, L) sysall(SYS_getrandom, B, L, 0)
+#define ENT_FINI() (void)0
 
+#elif defined(ENT_URANDOM)
+
+#define _ENT_IMPL
+#include <unistd.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
 
+#define ENT_DEFS int fd
+#define ENT_INIT() do {                           \
+  if ((fd = open("/dev/urandom", O_RDONLY)) < 0)  \
+    return -1;                                    \
+} while (0)
+#define ENT_READ(B, L) read(fd, B, L)
+#define ENT_FINI() (void) close(fd)
+
 #endif
 
+
+#include <ent/ent.h>
+
+#if defined(_ENT_IMPL)
+
+#include <assert.h>
+#include <errno.h>
+
+
 int
 ent_getentropy(void* buf, size_t len)
 {
   char *cuf = buf;
   int   ret;
-#if defined(_ENT_URANDOM)
-  int   fd;
-#endif
+  ENT_DEFS;
 
   assert(len <= 256);
   if (!len)
     return 0;
-#if defined(_ENT_URANDOM)
-  if ((fd = open("/dev/urandom", O_RDONLY)) < 0)
-    return -1;
-#endif
-  while (len &&
-#if defined(_ENT_GETRANDOM)
-          (ret = syscall(SYS_getrandom, cuf, len, 0)) != 0
-#elif defined(_ENT_URANDOM)
-          (ret = read(fd, cuf, len)) != 0
-#endif
-        ) {
+  ENT_INIT();
+  while (len && (ret = ENT_READ(cuf, len)) != 0) {
     if (ret < 0) {
       if (errno == EINTR)
         continue;
@@ -62,9 +61,7 @@ ent_getentropy(void* buf, size_t len)
     len -= ret;
     cuf += ret;
   }
-#if defined(_ENT_URANDOM)
-  (void) close(fd);
-#endif
+  ENT_FINI();
   if (!ret) {
     ret = -1;
     errno = EIO;
@@ -72,4 +69,4 @@ ent_getentropy(void* buf, size_t len)
   return ret < 0 ? ret : 0;
 }
 
-#endif /* _ENT_GETRANDOM || _ENT_URANDOM */
+#endif /* _ENT_IMPL */