diff --git a/include/sbi/riscv_asm.h b/include/sbi/riscv_asm.h
index ef48dc89..0cf3fc37 100644
--- a/include/sbi/riscv_asm.h
+++ b/include/sbi/riscv_asm.h
@@ -83,7 +83,7 @@
 
 #define csr_swap(csr, val)                                              \
 	({                                                              \
-		unsigned long __v = (unsigned long)(val);               \
+		register unsigned long __v = (unsigned long)(val);      \
 		__asm__ __volatile__("csrrw %0, " __ASM_STR(csr) ", %1" \
 				     : "=r"(__v)                        \
 				     : "rK"(__v)                        \
@@ -111,7 +111,7 @@
 
 #define csr_write(csr, val)                                        \
 	({                                                         \
-		unsigned long __v = (unsigned long)(val);          \
+		register unsigned long __v = (unsigned long)(val); \
 		__asm__ __volatile__("csrw " __ASM_STR(csr) ", %0" \
 				     :                             \
 				     : "rK"(__v)                   \
@@ -120,7 +120,7 @@
 
 #define csr_read_set(csr, val)                                          \
 	({                                                              \
-		unsigned long __v = (unsigned long)(val);               \
+		register unsigned long __v = (unsigned long)(val);      \
 		__asm__ __volatile__("csrrs %0, " __ASM_STR(csr) ", %1" \
 				     : "=r"(__v)                        \
 				     : "rK"(__v)                        \
@@ -130,7 +130,7 @@
 
 #define csr_set(csr, val)                                          \
 	({                                                         \
-		unsigned long __v = (unsigned long)(val);          \
+		register unsigned long __v = (unsigned long)(val); \
 		__asm__ __volatile__("csrs " __ASM_STR(csr) ", %0" \
 				     :                             \
 				     : "rK"(__v)                   \
@@ -139,7 +139,7 @@
 
 #define csr_read_clear(csr, val)                                        \
 	({                                                              \
-		unsigned long __v = (unsigned long)(val);               \
+		register unsigned long __v = (unsigned long)(val);      \
 		__asm__ __volatile__("csrrc %0, " __ASM_STR(csr) ", %1" \
 				     : "=r"(__v)                        \
 				     : "rK"(__v)                        \
@@ -149,7 +149,7 @@
 
 #define csr_clear(csr, val)                                        \
 	({                                                         \
-		unsigned long __v = (unsigned long)(val);          \
+		register unsigned long __v = (unsigned long)(val); \
 		__asm__ __volatile__("csrc " __ASM_STR(csr) ", %0" \
 				     :                             \
 				     : "rK"(__v)                   \