diff --git a/ext/sybase_ct/config.m4 b/ext/sybase_ct/config.m4
index 00d5b9cc199..72a982463e8 100644
--- a/ext/sybase_ct/config.m4
+++ b/ext/sybase_ct/config.m4
@@ -8,7 +8,7 @@ PHP_ARG_WITH(sybase-ct, for Sybase-CT support,
 
 if test "$PHP_SYBASE_CT" != "no"; then
 
-  if test "$PHP_SYBASE" != "no" && test "$ext_shared" = "no"; then
+  if test "$PHP_SYBASE" && test "$PHP_SYBASE" != "no" && test "$ext_shared" = "no"; then
     AC_MSG_ERROR([You can not use both --with-sybase and --with-sybase-ct in same build!])
   fi