diff --git a/config.m4 b/config.m4
index 130541f..b238017 100644
--- a/config.m4
+++ b/config.m4
@@ -5,7 +5,13 @@ dnl Comments in this file start with the string 'dnl'.
 dnl Remove where necessary. This file will not work
 dnl without editing.
 
-dnl If your extension references something external, use with:
+if test -z "$PHP_DEBUG"; then
+    AC_ARG_ENABLE(debug,
+    [   --enable-debug          compile with debugging symbols],[
+        PHP_DEBUG=$enableval
+    ],[ PHP_DEBUG=no
+    ])
+fi
 
 PHP_ARG_WITH(pdlib, for pdlib support,
 dnl Make sure that the comment is aligned:
@@ -15,8 +21,8 @@ if test "$PHP_PDLIB" != "no"; then
   dnl using C++11
   CXXFLAGS="-std=c++11"
   PHP_REQUIRE_CXX()
-  PHP_ADD_LIBRARY(stdc++, 1, DLIB_SHARED_LIBADD)
-  PHP_SUBST(DLIB_SHARED_LIBADD)
+  PHP_ADD_LIBRARY(stdc++, 1, PDLIB_SHARED_LIBADD)
+  PHP_SUBST(PDLIB_SHARED_LIBADD)
 
   pdlib_src_files="pdlib.cc \
   src/face_detection.cc"
@@ -38,7 +44,7 @@ if test "$PHP_PDLIB" != "no"; then
   else
      AC_MSG_ERROR(pkg-config not found)
   fi
-  PHP_EVAL_LIBLINE($LIBDLIB_LIBDIR, DLIB_SHARED_LIBADD)
+  PHP_EVAL_LIBLINE($LIBDLIB_LIBDIR, PDLIB_SHARED_LIBADD)
   PHP_EVAL_INCLINE($LIBDLIB_CFLAGS)
 
   PHP_NEW_EXTENSION(pdlib, $pdlib_src_files, $ext_shared,, -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1)