diff --git a/src/libunicode/CMakeLists.txt b/src/libunicode/CMakeLists.txt
index 25abbd1..d981da2 100644
--- a/src/libunicode/CMakeLists.txt
+++ b/src/libunicode/CMakeLists.txt
@@ -113,7 +113,13 @@ endif()
 
 
 if(LIBUNICODE_SIMD_IMPLEMENTATION STREQUAL "std" OR LIBUNICODE_SIMD_IMPLEMENTATION STREQUAL "intrinsics")
-    if(CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64" OR CMAKE_SYSTEM_PROCESSOR STREQUAL "AMD64")
+    # Normalize the processor name: it is "x86_64" on Linux, "AMD64" on Windows,
+    # and "amd64" on FreeBSD/other BSDs. A case-sensitive match missed the BSD
+    # spelling, so the SSE4.1/AVX flags below were never applied while the x86
+    # intrinsics in intrinsics.h (gated on __x86_64__) were still compiled,
+    # breaking the FreeBSD build with always_inline SSE4.1 errors.
+    string(TOLOWER "${CMAKE_SYSTEM_PROCESSOR}" _LIBUNICODE_PROCESSOR_LOWER)
+    if(_LIBUNICODE_PROCESSOR_LOWER STREQUAL "x86_64" OR _LIBUNICODE_PROCESSOR_LOWER STREQUAL "amd64")
         set(LIBUNICODE_SIMD_SOURCES
             simd_detector.cpp
             scan256.cpp