diff --git a/lldb/include/lldb/Utility/DataExtractor.h b/lldb/include/lldb/Utility/DataExtractor.h
--- a/lldb/include/lldb/Utility/DataExtractor.h
+++ b/lldb/include/lldb/Utility/DataExtractor.h
@@ -535,13 +535,13 @@
                              uint32_t bitfield_bit_size,
                              uint32_t bitfield_bit_offset) const;
 
-  /// Extract an signed integer of size \a byte_size from \a *offset_ptr, then
-  /// extract and signe extend the bitfield from this value if \a
+  /// Extract an signed integer of size \a size from \a *offset_ptr, then
+  /// extract and sign-extend the bitfield from this value if \a
   /// bitfield_bit_size is non-zero.
   ///
-  /// Extract a single signed integer value (sign extending if required) and
+  /// Extract a single signed integer value (sign-extending if required) and
   /// update the offset pointed to by \a offset_ptr. The size of the extracted
-  /// integer is specified by the \a byte_size argument. \a byte_size must
+  /// integer is specified by the \a size argument. \a size must
   /// have a value greater than or equal to one and less than or equal to
   /// eight since the return value is 64 bits wide.
   ///
diff --git a/lldb/source/Utility/DataExtractor.cpp b/lldb/source/Utility/DataExtractor.cpp
--- a/lldb/source/Utility/DataExtractor.cpp
+++ b/lldb/source/Utility/DataExtractor.cpp
@@ -604,6 +604,8 @@
 int64_t DataExtractor::GetMaxS64Bitfield(offset_t *offset_ptr, size_t size,
                                          uint32_t bitfield_bit_size,
                                          uint32_t bitfield_bit_offset) const {
+  assert(size >= 1 && "GetMaxS64Bitfield size must be >= 1");
+  assert(size <= 8 && "GetMaxS64Bitfield size must be <= 8");
   int64_t sval64 = GetMaxS64(offset_ptr, size);
   if (bitfield_bit_size > 0) {
     int32_t lsbcount = bitfield_bit_offset;
@@ -612,7 +614,7 @@
     if (lsbcount > 0)
       sval64 >>= lsbcount;
     uint64_t bitfield_mask =
-        ((static_cast<uint64_t>(1)) << bitfield_bit_size) - 1;
+        llvm::maskTrailingOnes<uint64_t>(bitfield_bit_size);
     sval64 &= bitfield_mask;
     // sign extend if needed
     if (sval64 & ((static_cast<uint64_t>(1)) << (bitfield_bit_size - 1)))
diff --git a/lldb/unittests/Utility/DataExtractorTest.cpp b/lldb/unittests/Utility/DataExtractorTest.cpp
--- a/lldb/unittests/Utility/DataExtractorTest.cpp
+++ b/lldb/unittests/Utility/DataExtractorTest.cpp
@@ -25,6 +25,9 @@
   offset = 0;
   ASSERT_EQ(buffer[1], BE.GetMaxU64Bitfield(&offset, sizeof(buffer), 8, 8));
   offset = 0;
+  ASSERT_EQ(static_cast<uint64_t>(0xEFCDAB8967452301),
+            LE.GetMaxU64Bitfield(&offset, sizeof(buffer), 64, 0));
+  offset = 0;
   ASSERT_EQ(static_cast<uint64_t>(0x0123456789ABCDEF),
             BE.GetMaxU64Bitfield(&offset, sizeof(buffer), 64, 0));
   offset = 0;
@@ -40,6 +43,12 @@
   offset = 0;
   ASSERT_EQ(int8_t(buffer[1]),
             BE.GetMaxS64Bitfield(&offset, sizeof(buffer), 8, 8));
+  offset = 0;
+  ASSERT_EQ(static_cast<int64_t>(0xEFCDAB8967452301),
+            LE.GetMaxS64Bitfield(&offset, sizeof(buffer), 64, 0));
+  offset = 0;
+  ASSERT_EQ(static_cast<int64_t>(0x0123456789ABCDEF),
+            BE.GetMaxS64Bitfield(&offset, sizeof(buffer), 64, 0));
 }
 
 TEST(DataExtractorTest, PeekData) {