diff --git a/ext/posh.h b/ext/posh.h
index 9c0e012..b122d58 100755
--- a/ext/posh.h
+++ b/ext/posh.h
@@ -524,6 +524,21 @@ Metrowerks:
 # define POSH_CPU_STRING "S/390"
 #endif
 
+#if defined __riscv && defined __riscv_xlen
+#  if __riscv_xlen == 32
+#    define POSH_CPU_RISCV32 1
+#    define POSH_CPU_STRING "RISCV32"
+#  elif __riscv_xlen == 64
+#    define POSH_CPU_RISCV64 1
+#    define POSH_CPU_STRING "RISCV64"
+#  elif __riscv_xlen == 128
+#    define POSH_CPU_RISCV128 1
+#    define POSH_CPU_STRING "RISCV128"
+#  else
+#    error "Unknown XLEN size!"
+#  endif
+#endif
+
 #if !defined POSH_CPU_STRING
 #  error POSH cannot determine target CPU
 #  define POSH_CPU_STRING "Unknown" /* this is here for Doxygen's benefit */