diff --git a/core/definitions.mk b/core/definitions.mk
index ded969b6eb..51eeadc4b5 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -3234,7 +3234,7 @@ endif
 ##
 ## $(1): path to validate
 define try-validate-path-is-subdir
-$(strip 
+$(strip \
     $(if $(filter /%,$(1)),
         $(1) starts with a slash
     )