diff --git a/Makefile b/Makefile
index fc3e1d45..c0efa629 100644
--- a/Makefile
+++ b/Makefile
@@ -157,7 +157,9 @@ else ifeq ($(PLATFORM),sun8i)
 	    # Otherwise we'll get compilation errors, check https://tls.mbed.org/kb/development/arm-thumb-error-r7-cannot-be-used-in-asm-here
 	    # quote: The assembly code in bn_mul.h is optimized for the ARM platform and uses some registers, including r7 to efficiently do an operation. GCC also uses r7 as the frame pointer under ARM Thumb assembly.
         MORE_CFLAGS += -fomit-frame-pointer
-endif
+	endif
+else
+$(error Unknown platform:$(PLATFORM))
 endif
 
 RM     = rm -f