https://github.com/ndilieto/uacme/pull/70

--- configure.ac.orig
+++ configure.ac
@@ -340,28 +340,31 @@ if test "x$OPT_UALPN" != "xno"; then
     AC_RUN_IFELSE([AC_LANG_SOURCE([#include <sys/mman.h>
                      int main() {return mmap(0, 4096, PROT_READ|PROT_WRITE,
                         MAP_ANON|MAP_SHARED, -1, 0) == MAP_FAILED;}])],
-        AC_DEFINE(HAVE_MAP_ANON, 1, [if mmap(MAP_ANON|MAP_SHARED) works])
-        AC_MSG_RESULT([yes]),
-        AC_MSG_RESULT([no])
-        AC_MSG_CHECKING([if mmap("/dev/zero", MAP_SHARED) works])
-        AC_RUN_IFELSE([AC_LANG_SOURCE([#include <sys/mman.h>
-                         #include <sys/stat.h>
-                         #include <fcntl.h>
-                         int main() {return mmap(0, 4096, PROT_READ|PROT_WRITE,
-                            MAP_ANON|MAP_SHARED, open("/dev/zero", O_RDWR), 0) ==
-                            MAP_FAILED;}])],
-            AC_DEFINE(HAVE_MAP_DEVZERO, 1, [if mmap("/dev/zero", MAP_SHARED) works])
-            AC_MSG_RESULT([yes]),
-            AC_MSG_RESULT([no])
-            AC_MSG_ERROR([ualpn requires MAP_ANON or mmap("/dev/zero", MAP_SHARED)])),
-        AC_COMPILE_IFELSE([AC_LANG_SOURCE([#include <sys/mman.h>
-                         int main() {return mmap(0, 4096, PROT_READ|PROT_WRITE,
-                            MAP_ANON|MAP_SHARED, -1, 0) == MAP_FAILED;}])],
+        [
             AC_DEFINE(HAVE_MAP_ANON, 1, [if mmap(MAP_ANON|MAP_SHARED) works])
-            AC_MSG_RESULT([yes]),
+            AC_MSG_RESULT([yes])
+        ], [
             AC_MSG_RESULT([no])
-            AC_MSG_NOTICE([falling back to mmap("/dev/zero", MAP_SHARED)])
-            AC_DEFINE(HAVE_MAP_DEVZERO, 1, [if mmap("/dev/zero", MAP_SHARED) works])))
+            AC_MSG_CHECKING([if mmap("/dev/zero", MAP_SHARED) works])
+            AC_RUN_IFELSE([AC_LANG_SOURCE([#include <sys/mman.h>
+                             #include <sys/stat.h>
+                             #include <fcntl.h>
+                             int main() {return mmap(0, 4096, PROT_READ|PROT_WRITE,
+                                MAP_ANON|MAP_SHARED, open("/dev/zero", O_RDWR), 0) ==
+                                MAP_FAILED;}])],
+                AC_DEFINE(HAVE_MAP_DEVZERO, 1, [if mmap("/dev/zero", MAP_SHARED) works])
+                AC_MSG_RESULT([yes]),
+                AC_MSG_RESULT([no])
+                AC_MSG_ERROR([ualpn requires MAP_ANON or mmap("/dev/zero", MAP_SHARED)])),
+            AC_COMPILE_IFELSE([AC_LANG_SOURCE([#include <sys/mman.h>
+                             int main() {return mmap(0, 4096, PROT_READ|PROT_WRITE,
+                                MAP_ANON|MAP_SHARED, -1, 0) == MAP_FAILED;}])],
+                AC_DEFINE(HAVE_MAP_ANON, 1, [if mmap(MAP_ANON|MAP_SHARED) works])
+                AC_MSG_RESULT([yes]),
+                AC_MSG_RESULT([no])
+                AC_MSG_NOTICE([falling back to mmap("/dev/zero", MAP_SHARED)])
+                AC_DEFINE(HAVE_MAP_DEVZERO, 1, [if mmap("/dev/zero", MAP_SHARED) works]))
+        ])
     AC_ARG_ENABLE(splice, AS_HELP_STRING([--disable-splice], [disable splice]))
     if test "x$enable_splice" != "xno"; then
         AC_CHECK_FUNCS([splice])