diff --git a/src/heap.cc b/src/heap.cc
index d813ed1dfd..7c9177859f 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -1669,7 +1669,7 @@ Object* Heap::AllocateSlicedString(String* buffer,
   int length = end - start;
 
   // If the resulting string is small make a sub string.
-  if (end - start <= String::kMinNonFlatLength) {
+  if (length <= String::kMinNonFlatLength) {
     return Heap::AllocateSubString(buffer, start, end);
   }
 
diff --git a/src/objects.h b/src/objects.h
index d367f815fd..b0d9d87099 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -4038,8 +4038,8 @@ class SlicedString: public String {
   // Layout description
 #if V8_HOST_ARCH_64_BIT
   // Optimizations expect buffer to be located at same offset as a ConsString's
-  // first substring. In 64 bit mode we have room for the size before the
-  // buffer.
+  // first substring. In 64 bit mode we have room for the start offset before
+  // the buffer.
   static const int kStartOffset = String::kSize;
   static const int kBufferOffset = kStartOffset + kIntSize;
   static const int kSize = kBufferOffset + kPointerSize;
diff --git a/src/x64/codegen-x64.cc b/src/x64/codegen-x64.cc
index 9060fe262e..be8e837ec7 100644
--- a/src/x64/codegen-x64.cc
+++ b/src/x64/codegen-x64.cc
@@ -5695,7 +5695,7 @@ void ToBooleanStub::Generate(MacroAssembler* masm) {
   __ and_(rcx, Immediate(kStringSizeMask));
   __ cmpq(rcx, Immediate(kShortStringTag));
   __ j(not_equal, &true_result);  // Empty string is always short.
-  __ movq(rdx, FieldOperand(rax, String::kLengthOffset));
+  __ movl(rdx, FieldOperand(rax, String::kLengthOffset));
   __ shr(rdx, Immediate(String::kShortLengthShift));
   __ j(zero, &false_result);
   __ jmp(&true_result);