diff --git a/rules.mk b/rules.mk
index d9b6b71f..1bb39ffc 100644
--- a/rules.mk
+++ b/rules.mk
@@ -8,17 +8,26 @@ MODULE := $(LOCAL_DIR)
 MODULE_CRATE_NAME := once_cell
 MODULE_RUST_CRATE_TYPES := rlib
 MODULE_SRCS := $(LOCAL_DIR)/src/lib.rs
-MODULE_ADD_IMPLICIT_DEPS := false
 MODULE_RUST_EDITION := 2021
 MODULE_RUSTFLAGS += \
 	--cfg 'feature="alloc"' \
 	--cfg 'feature="default"' \
 	--cfg 'feature="race"' \
-	--cfg 'feature="std"'
+
+ifeq ($(call TOBOOL,$(TRUSTY_USERSPACE)),true)
+
+MODULE_RUSTFLAGS += \
+	--cfg 'feature="std"' \
+
+else
+
+MODULE_ADD_IMPLICIT_DEPS := false

 MODULE_LIBRARY_DEPS := \
 	trusty/user/base/lib/liballoc-rust \
 	trusty/user/base/lib/libcompiler_builtins-rust \
 	trusty/user/base/lib/libcore-rust

+endif
+
 include make/library.mk