diff --git a/py/py.mk b/py/py.mk
index 2e7ffe9905e0c..22395b2e6157d 100644
--- a/py/py.mk
+++ b/py/py.mk
@@ -33,6 +33,8 @@ ifneq ($(USER_C_MODULES),)
 # pre-define USERMOD variables as expanded so that variables are immediate
 # expanded as they're added to them
 
+$(if $(wildcard $(USER_C_MODULES)/.),,$(error USER_C_MODULES doesn't exist: $(abspath $(USER_C_MODULES))))
+
 # C/C++ files that are included in the QSTR/module build
 SRC_USERMOD_C :=
 SRC_USERMOD_CXX :=