diff --git a/boards/cargo/riscv_bitmanip.toml b/boards/cargo/riscv_bitmanip.toml
new file mode 100644
index 0000000000..dc956678dd
--- /dev/null
+++ b/boards/cargo/riscv_bitmanip.toml
@@ -0,0 +1,11 @@
+# Licensed under the Apache License, Version 2.0 or the MIT License.
+# SPDX-License-Identifier: Apache-2.0 OR MIT
+# Copyright Tock Contributors 2024.
+
+# bitmanip instruction support for RISC-V.
+
+[build]
+rustflags = [
+  # These are the ratified bitmanip extensions supported by LLVM.
+  "-Ctarget-feature=+zba,+zbb,+zbc,+zbs",
+]
diff --git a/boards/opentitan/earlgrey-cw310/.cargo/config.toml b/boards/opentitan/earlgrey-cw310/.cargo/config.toml
index 7b1fa7be07..ede749d72a 100644
--- a/boards/opentitan/earlgrey-cw310/.cargo/config.toml
+++ b/boards/opentitan/earlgrey-cw310/.cargo/config.toml
@@ -6,6 +6,7 @@ include = [
   "../../../cargo/tock_flags.toml",
   "../../../cargo/unstable_flags.toml",
   "../../../cargo/riscv_flags.toml",
+  "../../../cargo/riscv_bitmanip.toml",
   "../../../cargo/virtual_function_elimination.toml",
   "../../../cargo/panic_abort_tests.toml",
 ]