diff --git a/README.md b/README.md
index 30c88d39..a143691f 100644
--- a/README.md
+++ b/README.md
@@ -25,6 +25,8 @@ This package contains:
 - libvorbisenc, a BSD-style license library that provides a simple,
   programmatic encoding setup interface
 
+- the generic scalar fallback used on non-x86 targets such as `riscv64`
+
 - example code making use of libogg, libvorbis, libvorbisfile and
   libvorbisenc
 
diff --git a/lib/os.h b/lib/os.h
index ae1e6f78..b84c985a 100644
--- a/lib/os.h
+++ b/lib/os.h
@@ -145,8 +145,10 @@ static __inline void vorbis_fpu_restore(vorbis_fpu_control fpu){
 
 
 /* Optimized code path for x86_64 builds. Uses SSE2 intrinsics. This can be
-   done safely because all x86_64 CPUs supports SSE2. */
-#if (defined(_MSC_VER) && (defined(_M_X64) && !defined(_M_ARM64EC))) || (defined(__GNUC__) && defined (__SSE2_MATH__))
+   done safely because all x86_64 CPUs supports SSE2. Keep it gated on x86_64
+   only, and explicitly step aside when a forced non-x86 target probe defines
+   __riscv on an x86_64 host for portability smoke testing. */
+#if (defined(_MSC_VER) && (defined(_M_X64) && !defined(_M_ARM64EC))) || (defined(__GNUC__) && defined(__x86_64__) && defined(__SSE2_MATH__) && !defined(__riscv))
 #  define VORBIS_FPU_CONTROL
 
 typedef ogg_int16_t vorbis_fpu_control;