diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 3dc4c0d31550..f46aa5602d74 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -1102,16 +1102,16 @@ early_param("riscv_isa_fallback", riscv_isa_fallback_setup);
 void __init riscv_fill_hwcap(void)
 {
 	char print_str[NUM_ALPHA_EXTS + 1];
-	unsigned long isa2hwcap[26] = {0};
+	unsigned long isa2hwcap[RISCV_ISA_EXT_BASE] = {0};
 	int i, j;
 
-	isa2hwcap['i' - 'a'] = COMPAT_HWCAP_ISA_I;
-	isa2hwcap['m' - 'a'] = COMPAT_HWCAP_ISA_M;
-	isa2hwcap['a' - 'a'] = COMPAT_HWCAP_ISA_A;
-	isa2hwcap['f' - 'a'] = COMPAT_HWCAP_ISA_F;
-	isa2hwcap['d' - 'a'] = COMPAT_HWCAP_ISA_D;
-	isa2hwcap['c' - 'a'] = COMPAT_HWCAP_ISA_C;
-	isa2hwcap['v' - 'a'] = COMPAT_HWCAP_ISA_V;
+	isa2hwcap[RISCV_ISA_EXT_i] = COMPAT_HWCAP_ISA_I;
+	isa2hwcap[RISCV_ISA_EXT_m] = COMPAT_HWCAP_ISA_M;
+	isa2hwcap[RISCV_ISA_EXT_a] = COMPAT_HWCAP_ISA_A;
+	isa2hwcap[RISCV_ISA_EXT_f] = COMPAT_HWCAP_ISA_F;
+	isa2hwcap[RISCV_ISA_EXT_d] = COMPAT_HWCAP_ISA_D;
+	isa2hwcap[RISCV_ISA_EXT_c] = COMPAT_HWCAP_ISA_C;
+	isa2hwcap[RISCV_ISA_EXT_v] = COMPAT_HWCAP_ISA_V;
 
 	if (!acpi_disabled) {
 		riscv_fill_hwcap_from_isa_string(isa2hwcap);