diff --git a/package/ruby/ruby.mk b/package/ruby/ruby.mk
index 243cd0b66c..298493c0f1 100644
--- a/package/ruby/ruby.mk
+++ b/package/ruby/ruby.mk
@@ -30,7 +30,7 @@ endif
 RUBY_CONF_ENV = CFLAGS="$(RUBY_CFLAGS)"
 
 ifeq ($(BR2_bfin),y)
-RUBY_CONF_ENV = ac_cv_func_dl_iterate_phdr=no
+RUBY_CONF_ENV += ac_cv_func_dl_iterate_phdr=no
 # Blackfin doesn't have FFI closure support, needed by the fiddle
 # extension.
 RUBY_CONF_OPTS += --with-out-ext=fiddle