diff --git a/acinclude.m4 b/acinclude.m4
index 1ad488cd86a..531f401ef94 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -1573,7 +1573,7 @@ AC_DEFUN([PHP_CHECK_LIBRARY], [
   ],[
     LDFLAGS=$save_old_LDFLAGS
     ext_shared=$save_ext_shared
-    unset ac_cv_func_$1
+    unset ac_cv_lib_$1[]_$2
     $4
   ])dnl
 ])
diff --git a/ext/dba/config.m4 b/ext/dba/config.m4
index 7f3c359a8ab..103e2e1bb0e 100644
--- a/ext/dba/config.m4
+++ b/ext/dba/config.m4
@@ -116,7 +116,6 @@ AC_ARG_WITH(gdbm,
     done
 
     if test -n "$THIS_INCLUDE"; then
-      unset ac_cv_lib_gdbm_gdbm_open
       PHP_CHECK_LIBRARY(gdbm, gdbm_open, [
         AC_DEFINE_UNQUOTED(GDBM_INCLUDE_FILE, "$THIS_INCLUDE", [ ])
         AC_DEFINE(DBA_GDBM, 1, [ ]) 
diff --git a/ext/mcrypt/config.m4 b/ext/mcrypt/config.m4
index 0e162c5997b..c93e040bcac 100644
--- a/ext/mcrypt/config.m4
+++ b/ext/mcrypt/config.m4
@@ -39,8 +39,6 @@ if test "$PHP_MCRYPT" != "no"; then
     PHP_ADD_LIBRARY(ltdl,, MCRYPT_SHARED_LIBADD)
     AC_DEFINE(HAVE_LIBMCRYPT,1,[ ])
   ],[
-    unset found
-    unset ac_cv_lib_mcrypt_mcrypt_module_open
     PHP_CHECK_LIBRARY(mcrypt, mcrypt_module_open,
     [
       AC_DEFINE(HAVE_LIBMCRYPT,1,[ ])