diff --git a/include/sbi/riscv_asm.h b/include/sbi/riscv_asm.h
index 04502e1..c3d5985 100644
--- a/include/sbi/riscv_asm.h
+++ b/include/sbi/riscv_asm.h
@@ -159,8 +159,16 @@ void csr_write_num(int csr_num, unsigned long val);
 		__asm__ __volatile__("wfi" ::: "memory"); \
 	} while (0)
 
-/* Determine CPU extension, return non-zero support */
-int misa_extension(char ext);
+
+/* determine CPU extension, return non-zero support */
+int misa_extension_imp(char ext);
+
+#define misa_extension(c)\
+({\
+	_Static_assert(((c >= 'A') && (c <= 'Z')),\
+		"The parameter of misa_extension must be [A-Z]");\
+	misa_extension_imp(c);\
+})
 
 /* Get MXL field of misa, return -1 on error */
 int misa_xlen(void);
@@ -170,7 +178,7 @@ static inline void misa_string(char *out, unsigned int out_sz)
 	unsigned long i;
 
 	for (i = 0; i < 26; i++) {
-		if (misa_extension('A' + i)) {
+		if (misa_extension_imp('A' + i)) {
 			*out = 'A' + i;
 			out++;
 		}
diff --git a/lib/sbi/riscv_asm.c b/lib/sbi/riscv_asm.c
index d16e32a..7b612d4 100644
--- a/lib/sbi/riscv_asm.c
+++ b/lib/sbi/riscv_asm.c
@@ -12,7 +12,8 @@
 #include <sbi/sbi_error.h>
 #include <sbi/sbi_platform.h>
 
-int misa_extension(char ext)
+/* determine CPU extension, return non-zero support */
+int misa_extension_imp(char ext)
 {
 	unsigned long misa = csr_read(CSR_MISA);