diff --git a/ext/json/ext/simd/conf.rb b/ext/json/ext/simd/conf.rb
index 76f774bc9..9b87473d5 100644
--- a/ext/json/ext/simd/conf.rb
+++ b/ext/json/ext/simd/conf.rb
@@ -1,16 +1,15 @@
 case RbConfig::CONFIG['host_cpu']
 when /^(arm|aarch64)/
   # Try to compile a small program using NEON instructions
-  header, type, init, extra = 'arm_neon.h', 'uint8x16_t', 'vdupq_n_u8(32)', nil
+  header, type, init = 'arm_neon.h', 'uint8x16_t', 'vdupq_n_u8(32)'
 when /^(x86_64|x64)/
-  header, type, init, extra = 'x86intrin.h', '__m128i', '_mm_set1_epi8(32)', 'if (__builtin_cpu_supports("sse2")) { printf("OK"); }'
+  header, type, init = 'x86intrin.h', '__m128i', '_mm_set1_epi8(32)'
 end
 if header
   if have_header(header) && try_compile(<<~SRC, '-Werror=implicit-function-declaration')
       #{cpp_include(header)}
       int main(int argc, char **argv) {
         #{type} test = #{init};
-        #{extra}
         if (argc > 100000) printf("%p", &test);
         return 0;
       }
@@ -20,5 +19,3 @@
     puts "Disable SIMD"
   end
 end
-
-have_header('cpuid.h')
diff --git a/ext/json/ext/simd/simd.h b/ext/json/ext/simd/simd.h
index 611b41b06..2f3f838a9 100644
--- a/ext/json/ext/simd/simd.h
+++ b/ext/json/ext/simd/simd.h
@@ -143,7 +143,6 @@ ALWAYS_INLINE(static) int string_scan_simd_neon(const char **ptr, const char *en
 #define HAVE_SIMD 1
 #define HAVE_SIMD_SSE2 1
 
-#ifdef HAVE_CPUID_H
 #define FIND_SIMD_IMPLEMENTATION_DEFINED 1
 
 #if defined(__clang__) || defined(__GNUC__)
@@ -182,17 +181,10 @@ ALWAYS_INLINE(static) TARGET_SSE2 int string_scan_simd_sse2(const char **ptr, co
     return 0;
 }
 
-#include <cpuid.h>
-#endif /* HAVE_CPUID_H */
-
 static inline SIMD_Implementation find_simd_implementation(void)
 {
-    // TODO Revisit. I think the SSE version now only uses SSE2 instructions.
-    if (__builtin_cpu_supports("sse2")) {
-        return SIMD_SSE2;
-    }
-
-    return SIMD_NONE;
+    // SSE2 is part of the x86-64 baseline.
+    return SIMD_SSE2;
 }
 
 #endif /* HAVE_X86INTRIN_H */