diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index ee2523f66b..5702c53c62 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -489,6 +489,9 @@ static void riscv_cpu_realize(DeviceState *dev, Error **errp)
         if (cpu->cfg.ext_h) {
             target_misa |= RVH;
         }
+        if (cpu->cfg.ext_b) {
+            target_misa |= RVB;
+        }
         if (cpu->cfg.ext_v) {
             target_misa |= RVV;
             if (!is_power_of_2(cpu->cfg.vlen)) {
@@ -559,6 +562,7 @@ static Property riscv_cpu_properties[] = {
     DEFINE_PROP_BOOL("s", RISCVCPU, cfg.ext_s, true),
     DEFINE_PROP_BOOL("u", RISCVCPU, cfg.ext_u, true),
     /* This is experimental so mark with 'x-' */
+    DEFINE_PROP_BOOL("x-b", RISCVCPU, cfg.ext_b, false),
     DEFINE_PROP_BOOL("x-h", RISCVCPU, cfg.ext_h, false),
     DEFINE_PROP_BOOL("x-v", RISCVCPU, cfg.ext_v, false),
     DEFINE_PROP_BOOL("Counters", RISCVCPU, cfg.ext_counters, true),
diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index c0c99c3d8d..de9262c930 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -286,6 +286,7 @@ struct RISCVCPU {
         bool ext_f;
         bool ext_d;
         bool ext_c;
+        bool ext_b;
         bool ext_s;
         bool ext_u;
         bool ext_h;