diff --git a/libc/include/bits/fenv_riscv64.h b/libc/include/bits/fenv_riscv64.h
index 2149f608378957df4635dfecbabb137549162d53..69232bb936733f97f7f15428c755984a3561668d 100644
--- a/libc/include/bits/fenv_riscv64.h
+++ b/libc/include/bits/fenv_riscv64.h
@@ -43,10 +43,17 @@ typedef unsigned int fenv_t;
 #define FE_INVALID    0x10
 #define FE_ALL_EXCEPT (FE_DIVBYZERO | FE_INEXACT | FE_INVALID | FE_OVERFLOW | FE_UNDERFLOW)
 
-/* Rounding modes. */
+/*
+ * Rounding modes.
+ * Currently, we have not supported FE_TOMM (Round to Nearest, ties to Max Magnitude).
+ */
 #define FE_TONEAREST  0x0
 #define FE_TOWARDZERO 0x1
 #define FE_DOWNWARD   0x2
 #define FE_UPWARD     0x3
+#define FE_TOMM       0x4
+
+#define FE_ROUNDMODE_MIN FE_TONEAREST
+#define FE_ROUNDMODE_MAX FE_UPWARD
 
 __END_DECLS
diff --git a/libm/riscv64/fenv.c b/libm/riscv64/fenv.c
index a4dfe15aee260713462068016b912aa5cd80a4ba..0af7a0081bb1a764ed87bcf88eea233e148d4051 100644
--- a/libm/riscv64/fenv.c
+++ b/libm/riscv64/fenv.c
@@ -95,6 +95,9 @@ int fegetround(void)
 
 int fesetround(int round)
 {
+  if (round < FE_ROUNDMODE_MIN || round > FE_ROUNDMODE_MAX) {
+    return -1;
+  }
   asm volatile ("fsrm %z0" : : "r" (round));
   return 0;
 }