diff --git a/auto/unix b/auto/unix
index e24099cc3..dbc0f0e42 100755
--- a/auto/unix
+++ b/auto/unix
@@ -261,7 +261,7 @@ ngx_feature_run=no
 ngx_feature_incs="#include <dlfcn.h>"
 ngx_feature_path=
 ngx_feature_libs=
-ngx_feature_test="dlopen(NULL, RTLD_NOW | RTLD_GLOBAL); dlsym(NULL, NULL)"
+ngx_feature_test="dlopen(NULL, RTLD_NOW | RTLD_GLOBAL); dlsym(NULL, \"\")"
 . auto/feature