diff --git a/include/aws/checksums/private/crc64_priv.h b/include/aws/checksums/private/crc64_priv.h
index 29b8820..39090e0 100644
--- a/include/aws/checksums/private/crc64_priv.h
+++ b/include/aws/checksums/private/crc64_priv.h
@@ -15,16 +15,18 @@ AWS_EXTERN_C_BEGIN
 
 AWS_CHECKSUMS_API uint64_t aws_checksums_crc64xz_sw(const uint8_t *input, int length, uint64_t prev_crc64);
 
-#if defined(AWS_ARCH_INTEL_X64) && defined(AWS_HAVE_CLMUL) && !(defined(_MSC_VER) && _MSC_VER < 1920)
+#if defined(AWS_USE_CPU_EXTENSIONS) && defined(AWS_ARCH_INTEL_X64) && defined(AWS_HAVE_CLMUL) &&                       \
+    !(defined(_MSC_VER) && _MSC_VER < 1920)
 uint64_t aws_checksums_crc64xz_intel_clmul(const uint8_t *input, int length, uint64_t previous_crc_64);
 #endif /* defined(AWS_ARCH_INTEL_X64) && defined(AWS_HAVE_CLMUL) && !(defined(_MSC_VER) && _MSC_VER < 1920) */
 
-#if defined(AWS_ARCH_INTEL_X64) && defined(AWS_HAVE_AVX2_INTRINSICS) && !(defined(_MSC_VER) && _MSC_VER < 1920)
+#if defined(AWS_USE_CPU_EXTENSIONS) && defined(AWS_ARCH_INTEL_X64) && defined(AWS_HAVE_AVX2_INTRINSICS) &&             \
+    !(defined(_MSC_VER) && _MSC_VER < 1920)
 uint64_t aws_checksums_crc64xz_intel_avx512(const uint8_t *input, int length, uint64_t previous_crc_64);
 #endif /* defined(AWS_ARCH_INTEL_X64) && defined(AWS_HAVE_AVX2_INTRINSICS) && !(defined(_MSC_VER) && _MSC_VER < 1920)  \
         */
 
-#if defined(AWS_ARCH_ARM64)
+#if defined(AWS_USE_CPU_EXTENSIONS) && defined(AWS_ARCH_ARM64)
 uint64_t aws_checksums_crc64xz_arm_pmull(const uint8_t *input, int length, uint64_t previous_crc_64);
 #endif /* INTPTR_MAX == INT64_MAX && defined(AWS_HAVE_ARMv8_1) */
 
diff --git a/include/aws/checksums/private/crc_priv.h b/include/aws/checksums/private/crc_priv.h
index 93f4d4d..678677d 100644
--- a/include/aws/checksums/private/crc_priv.h
+++ b/include/aws/checksums/private/crc_priv.h
@@ -20,10 +20,10 @@ AWS_CHECKSUMS_API uint32_t aws_checksums_crc32_sw(const uint8_t *input, int leng
 /* Computes the Castagnoli CRC32c (iSCSI) using a (slow) reference implementation. */
 AWS_CHECKSUMS_API uint32_t aws_checksums_crc32c_sw(const uint8_t *input, int length, uint32_t previousCrc32c);
 
-#if defined(AWS_ARCH_ARM64)
+#if defined(AWS_USE_CPU_EXTENSIONS) && defined(AWS_ARCH_ARM64)
 uint32_t aws_checksums_crc32_armv8(const uint8_t *input, int length, uint32_t previous_crc32);
 uint32_t aws_checksums_crc32c_armv8(const uint8_t *input, int length, uint32_t previous_crc32c);
-#elif defined(AWS_ARCH_INTEL)
+#elif defined(AWS_USE_CPU_EXTENSIONS) && defined(AWS_ARCH_INTEL)
 #    if defined(AWS_ARCH_INTEL_X64)
 typedef uint64_t *slice_ptr_type;
 typedef uint64_t slice_ptr_int_type;
diff --git a/source/crc64.c b/source/crc64.c
index 4a41ad9..5976275 100644
--- a/source/crc64.c
+++ b/source/crc64.c
@@ -21,10 +21,11 @@ checksums_maxks_shifts_type aws_checksums_masks_shifts = {
 
 AWS_ALIGNED_TYPEDEF(aws_checksums_crc64_constants_t, cheksums_constants, 16);
 
+/* clang-format off */
+
 // Pre-computed bit-reflected constants for CRC64XZ
 // The actual exponents are reduced by 1 to compensate for bit-reflection (e.g. x^1024 is actually x^1023)
 cheksums_constants aws_checksums_crc64xz_constants = {
-    /* clang-format off */
 
     .x2048 =
         {0x8260adf2381ad81c,
@@ -84,9 +85,9 @@ cheksums_constants aws_checksums_crc64xz_constants = {
             {0xb91b6176fc36363f, 0xdda9f27ee08373ad}, // 13 trailing bytes: x^168 mod P(x) / x^104 mod P(x)
             {0x4dcec64d2edf818c, 0x0dd9b4240837fd99}, // 14 trailing bytes: x^176 mod P(x) / x^112 mod P(x)
             {0x4550ddde9a383296, 0xf075e4ae5e05bdff}  // 15 trailing bytes: x^184 mod P(x) / x^120 mod P(x)
-        },                                           
-    /* clang-format on */
+        },                                            //
 };
+/* clang-format on */
 
 static uint64_t (*s_crc64xz_fn_ptr)(const uint8_t *input, int length, uint64_t prev_crc64) = 0;