diff --git a/extlib/rapidjson/include/rapidjson/internal/biginteger.h b/extlib/rapidjson/include/rapidjson/internal/biginteger.h
index 9d3e88c99..a114198c5 100644
--- a/extlib/rapidjson/include/rapidjson/internal/biginteger.h
+++ b/extlib/rapidjson/include/rapidjson/internal/biginteger.h
@@ -17,9 +17,14 @@
 
 #include "../rapidjson.h"
 
-#if defined(_MSC_VER) && defined(_M_AMD64)
+// rom-properties: Use softintrin.lib on ARM64EC. (ported from upstream)
+#if defined(_MSC_VER) && !defined(__INTEL_COMPILER) && defined(_M_AMD64)
 #include <intrin.h> // for _umul128
+#if !defined(_M_ARM64EC)
 #pragma intrinsic(_umul128)
+#else
+#pragma comment(lib,"softintrin")
+#endif
 #endif
 
 RAPIDJSON_NAMESPACE_BEGIN
diff --git a/extlib/rapidjson/include/rapidjson/internal/diyfp.h b/extlib/rapidjson/include/rapidjson/internal/diyfp.h
index c9fefdc61..30647ffdb 100644
--- a/extlib/rapidjson/include/rapidjson/internal/diyfp.h
+++ b/extlib/rapidjson/include/rapidjson/internal/diyfp.h
@@ -21,10 +21,15 @@
 
 #include "../rapidjson.h"
 
-#if defined(_MSC_VER) && defined(_M_AMD64)
+// rom-properties: Use softintrin.lib on ARM64EC. (ported from upstream)
+#if defined(_MSC_VER) && !defined(__INTEL_COMPILER) && defined(_M_AMD64)
 #include <intrin.h>
 #pragma intrinsic(_BitScanReverse64)
+#if !defined(_M_ARM64EC)
 #pragma intrinsic(_umul128)
+#else
+#pragma comment(lib,"softintrin")
+#endif
 #endif
 
 RAPIDJSON_NAMESPACE_BEGIN