diff --git a/Makefile b/Makefile
index 362df202fb8a..93831019c17b 100644
--- a/Makefile
+++ b/Makefile
@@ -447,6 +447,8 @@ ifneq ($(filter %/,$(LLVM)),)
 LLVM_PREFIX := $(LLVM)
 else ifneq ($(filter -%,$(LLVM)),)
 LLVM_SUFFIX := $(LLVM)
+else ifneq ($(LLVM),1)
+$(error Invalid value for LLVM, see Documentation/kbuild/llvm.rst)
 endif
 
 HOSTCC	= $(LLVM_PREFIX)clang$(LLVM_SUFFIX)