diff --git a/llvm/lib/Support/BLAKE3/blake3_impl.h b/llvm/lib/Support/BLAKE3/blake3_impl.h
--- a/llvm/lib/Support/BLAKE3/blake3_impl.h
+++ b/llvm/lib/Support/BLAKE3/blake3_impl.h
@@ -64,7 +64,11 @@
 #if !defined(BLAKE3_USE_NEON) 
   // If BLAKE3_USE_NEON not manually set, autodetect based on AArch64ness
   #if defined(IS_AARCH64)
-    #define BLAKE3_USE_NEON 1
+    #if defined(__ARM_BIG_ENDIAN)
+      #define BLAKE3_USE_NEON 0
+    #else
+      #define BLAKE3_USE_NEON 1
+    #endif
   #else
     #define BLAKE3_USE_NEON 0
   #endif