diff --git a/core/definitions.mk b/core/definitions.mk
index ce71f45..94ceb76 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -1152,7 +1152,7 @@
 @mkdir -p $(dir $@)
 $(hide) $(RELATIVE_PWD) $(PRIVATE_CXX) \
 	$(addprefix -I , $(PRIVATE_C_INCLUDES)) \
-	$(shell cat $(PRIVATE_IMPORT_INCLUDES)) \
+	$$(cat $(PRIVATE_IMPORT_INCLUDES)) \
 	$(addprefix -isystem ,\
 	    $(if $(PRIVATE_NO_DEFAULT_COMPILER_FLAGS),, \
 	        $(filter-out $(PRIVATE_C_INCLUDES), \
@@ -1184,7 +1184,7 @@
 @mkdir -p $(dir $@)
 $(hide) $(RELATIVE_PWD) $(PRIVATE_CC) \
 	$(addprefix -I , $(PRIVATE_C_INCLUDES)) \
-	$(shell cat $(PRIVATE_IMPORT_INCLUDES)) \
+	$$(cat $(PRIVATE_IMPORT_INCLUDES)) \
 	$(addprefix -isystem ,\
 	    $(if $(PRIVATE_NO_DEFAULT_COMPILER_FLAGS),, \
 	        $(filter-out $(PRIVATE_C_INCLUDES), \
@@ -1259,7 +1259,7 @@
 @mkdir -p $(dir $@)
 $(hide) $(RELATIVE_PWD) $(PRIVATE_CXX) \
 	$(addprefix -I , $(PRIVATE_C_INCLUDES)) \
-	$(shell cat $(PRIVATE_IMPORT_INCLUDES)) \
+	$$(cat $(PRIVATE_IMPORT_INCLUDES)) \
 	$(addprefix -isystem ,\
 	    $(if $(PRIVATE_NO_DEFAULT_COMPILER_FLAGS),, \
 	        $(filter-out $(PRIVATE_C_INCLUDES), \
@@ -1289,7 +1289,7 @@
 @mkdir -p $(dir $@)
 $(hide) $(RELATIVE_PWD) $(PRIVATE_CC) \
 	$(addprefix -I , $(PRIVATE_C_INCLUDES)) \
-	$(shell cat $(PRIVATE_IMPORT_INCLUDES)) \
+	$$(cat $(PRIVATE_IMPORT_INCLUDES)) \
 	$(addprefix -isystem ,\
 	    $(if $(PRIVATE_NO_DEFAULT_COMPILER_FLAGS),, \
 	        $(filter-out $(PRIVATE_C_INCLUDES), \