diff --git a/ext/pdo_dblib/config.m4 b/ext/pdo_dblib/config.m4
index 0adf020c295..1b68a9913b3 100644
--- a/ext/pdo_dblib/config.m4
+++ b/ext/pdo_dblib/config.m4
@@ -4,14 +4,14 @@ PHP_ARG_WITH([pdo-dblib],
     [PDO: DBLIB-DB support. DIR is the FreeTDS home directory])])
 
 if test "$PHP_PDO_DBLIB" != "no"; then
-  if test "$PHP_PDO_DBLIB" = "yes"; then
+  AS_VAR_IF([PHP_PDO_DBLIB], [yes], [
     dnl FreeTDS must be on the default system include/library path.
     dnl Only perform a sanity check that this is really the case.
     PHP_CHECK_LIBRARY([sybdb], [dbsqlexec],
       [],
       [AC_MSG_FAILURE([Cannot find FreeTDS in known installation directories.])])
     PHP_ADD_LIBRARY([sybdb],, [PDO_DBLIB_SHARED_LIBADD])
-  elif test "$PHP_PDO_DBLIB" != "no"; then
+  ], [
     if test -f $PHP_PDO_DBLIB/include/sybdb.h; then
       PDO_FREETDS_INSTALLATION_DIR=$PHP_PDO_DBLIB
       PDO_FREETDS_INCLUDE_DIR=$PHP_PDO_DBLIB/include
@@ -32,7 +32,7 @@ if test "$PHP_PDO_DBLIB" != "no"; then
     PHP_ADD_LIBRARY_WITH_PATH([sybdb],
       [$PDO_FREETDS_INSTALLATION_DIR/$PHP_LIBDIR],
       [PDO_DBLIB_SHARED_LIBADD])
-  fi
+  ])
 
   PHP_CHECK_PDO_INCLUDES