diff --git a/include/llvm/IR/Attributes.h b/include/llvm/IR/Attributes.h
index 297abb96486..89a73d61824 100644
--- a/include/llvm/IR/Attributes.h
+++ b/include/llvm/IR/Attributes.h
@@ -353,7 +353,7 @@ public:
   unsigned getNumSlots() const;
 
   /// \brief Return the index for the given slot.
-  unsigned getSlotIndex(unsigned Slot) const;
+  uint64_t getSlotIndex(unsigned Slot) const;
 
   /// \brief Return the attributes at the given slot.
   AttributeSet getSlotAttributes(unsigned Slot) const;
diff --git a/lib/IR/Attributes.cpp b/lib/IR/Attributes.cpp
index 81390f0bc14..8e64a49c47a 100644
--- a/lib/IR/Attributes.cpp
+++ b/lib/IR/Attributes.cpp
@@ -694,7 +694,7 @@ unsigned AttributeSet::getNumSlots() const {
   return pImpl ? pImpl->getNumAttributes() : 0;
 }
 
-unsigned AttributeSet::getSlotIndex(unsigned Slot) const {
+uint64_t AttributeSet::getSlotIndex(unsigned Slot) const {
   assert(pImpl && Slot < pImpl->getNumAttributes() &&
          "Slot # out of range!");
   return pImpl->getSlotIndex(Slot);