--- CMakeLists.txt.orig	2026-08-21 02:05:04.000000000 -0600
+++ CMakeLists.txt	2026-08-21 02:19:08.000000000 -0600
@@ -155,6 +155,13 @@
             # Set LIBDEFLATE_ASSEMBLER_DOES_NOT_SUPPORT_AVX_VNNI if needed.
             check_assembler_support(AVX_VNNI "{vex} vpdpbusd %ymm0, %ymm0, %ymm0")
         endif()
+	# GCC 4.9 is the minimum, and supports all of these instructions.
+        # Set LIBDEFLATE_ASSEMBLER_DOES_NOT_SUPPORT_AVX2 if needed.
+        check_assembler_support(AVX2 "vpxor %ymm0, %ymm0, %ymm0")
+        # Set LIBDEFLATE_ASSEMBLER_DOES_NOT_SUPPORT_PCLMULQDQ if needed.
+        check_assembler_support(PCLMULQDQ "pclmulqdq $0, %xmm0, %xmm0")
+        # Set LIBDEFLATE_ASSEMBLER_DOES_NOT_SUPPORT_BMI2 if needed.
+        check_assembler_support(BMI2 "shlx %eax, %eax, %eax")
     elseif(${machine} MATCHES "^aarch64")
         if(${CMAKE_C_COMPILER_VERSION} VERSION_GREATER_EQUAL 8.1)
             # Set LIBDEFLATE_ASSEMBLER_DOES_NOT_SUPPORT_DOTPROD if needed.
--- lib/x86/adler32_impl.h.orig	2026-08-14 23:15:39.000000000 -0600
+++ lib/x86/adler32_impl.h	2026-08-14 23:17:32.000000000 -0600
@@ -40,6 +40,7 @@
 #  define USE_AVX512		0
 #  include "adler32_template.h"
 
+#  if !defined(LIBDEFLATE_ASSEMBLER_DOES_NOT_SUPPORT_AVX2)
 #  define adler32_x86_avx2	adler32_x86_avx2
 #  define SUFFIX			   _avx2
 #  define ATTRIBUTES		_target_attribute("avx2")
@@ -48,6 +49,7 @@
 #  define USE_AVX512		0
 #  include "adler32_template.h"
 #endif
+#endif
 
 /*
  * AVX-VNNI implementation.  This is used on CPUs that have AVX2 and AVX-VNNI
--- lib/x86/crc32_impl.h.orig	2026-08-14 23:51:25.000000000 -0600
+++ lib/x86/crc32_impl.h	2026-08-14 23:56:10.000000000 -0600
@@ -48,6 +48,7 @@
  * PCLMULQDQ implementation.  This targets PCLMULQDQ+SSE4.1, since in practice
  * all CPUs that support PCLMULQDQ also support SSE4.1.
  */
+#if !defined(LIBDEFLATE_ASSEMBLER_DOES_NOT_SUPPORT_PCLMULQDQ)
 #  define crc32_x86_pclmulqdq	crc32_x86_pclmulqdq
 #  define SUFFIX			 _pclmulqdq
 #  define ATTRIBUTES		_target_attribute("pclmul,sse4.1")
@@ -67,6 +68,7 @@
 #  define USE_AVX512		0
 #  include "crc32_pclmul_template.h"
 #endif
+#endif
 
 /*
  * VPCLMULQDQ/AVX2 implementation.  This is used on CPUs that have AVX2 and
--- lib/x86/decompress_impl.h.orig	2026-08-15 00:39:16.000000000 -0600
+++ lib/x86/decompress_impl.h	2026-08-15 00:40:00.000000000 -0600
@@ -16,6 +16,7 @@
  * intrinsics.  It seems to be fixed in VS2022.  Hence, use MSVC_PREREQ(1930).
  */
 #if defined(__GNUC__) || defined(__clang__) || MSVC_PREREQ(1930)
+#if !defined(LIBDEFLATE_ASSEMBLER_DOES_NOT_SUPPORT_BMI2) 
 #  define deflate_decompress_bmi2	deflate_decompress_bmi2
 #  define FUNCNAME			deflate_decompress_bmi2
 #  define ATTRIBUTES			_target_attribute("bmi2")
@@ -38,6 +39,7 @@
 #  endif
 #  include "../decompress_template.h"
 #endif
+#endif
 
 #if defined(deflate_decompress_bmi2) && HAVE_BMI2_NATIVE
 #define DEFAULT_IMPL	deflate_decompress_bmi2