Index: lib/IR/Attributes.cpp
===================================================================
--- lib/IR/Attributes.cpp
+++ lib/IR/Attributes.cpp
@@ -543,17 +543,17 @@
 AttributeSet AttributeSet::removeAttribute(LLVMContext &C,
                                              Attribute::AttrKind Kind) const {
   if (!hasAttribute(Kind)) return *this;
-  AttrBuilder B;
-  B.addAttribute(Kind);
-  return removeAttributes(C, B);
+  AttrBuilder B(*this);
+  B.removeAttribute(Kind);
+  return get(C, B);
 }
 
 AttributeSet AttributeSet::removeAttribute(LLVMContext &C,
                                              StringRef Kind) const {
   if (!hasAttribute(Kind)) return *this;
-  AttrBuilder B;
-  B.addAttribute(Kind);
-  return removeAttributes(C, B);
+  AttrBuilder B(*this);
+  B.removeAttribute(Kind);
+  return get(C, B);
 }
 
 AttributeSet AttributeSet::removeAttributes(LLVMContext &C,
@@ -1098,17 +1098,37 @@
 AttributeList AttributeList::removeAttribute(LLVMContext &C, unsigned Index,
                                              Attribute::AttrKind Kind) const {
   if (!hasAttribute(Index, Kind)) return *this;
-  AttrBuilder B;
-  B.addAttribute(Kind);
-  return removeAttributes(C, Index, B);
+  if (!pImpl)
+    return AttributeList();
+
+  Index = attrIdxToArrayIdx(Index);
+  SmallVector<AttributeSet, 4> AttrSets(this->begin(), this->end());
+  if (Index >= AttrSets.size())
+    AttrSets.resize(Index + 1);
+
+  AttrBuilder B(AttrSets[Index]);
+  B.removeAttribute(Kind);
+  AttrSets[Index] = AttributeSet::get(C, B);
+
+  return getImpl(C, AttrSets);
 }
 
 AttributeList AttributeList::removeAttribute(LLVMContext &C, unsigned Index,
                                              StringRef Kind) const {
   if (!hasAttribute(Index, Kind)) return *this;
-  AttrBuilder B;
-  B.addAttribute(Kind);
-  return removeAttributes(C, Index, B);
+  if (!pImpl)
+    return AttributeList();
+
+  Index = attrIdxToArrayIdx(Index);
+  SmallVector<AttributeSet, 4> AttrSets(this->begin(), this->end());
+  if (Index >= AttrSets.size())
+    AttrSets.resize(Index + 1);
+
+  AttrBuilder B(AttrSets[Index]);
+  B.removeAttribute(Kind);
+  AttrSets[Index] = AttributeSet::get(C, B);
+
+  return getImpl(C, AttrSets);
 }
 
 AttributeList
@@ -1117,10 +1137,6 @@
   if (!pImpl)
     return AttributeList();
 
-  // FIXME it is not obvious how this should work for alignment.
-  // For now, say we can't pass in alignment, which no current use does.
-  assert(!AttrsToRemove.hasAlignmentAttr() && "Attempt to change alignment!");
-
   Index = attrIdxToArrayIdx(Index);
   SmallVector<AttributeSet, 4> AttrSets(this->begin(), this->end());
   if (Index >= AttrSets.size())
Index: unittests/IR/AttributesTest.cpp
===================================================================
--- unittests/IR/AttributesTest.cpp
+++ unittests/IR/AttributesTest.cpp
@@ -63,6 +63,23 @@
   EXPECT_TRUE(AL.hasFnAttribute(Attribute::NoReturn));
 }
 
+TEST(Attributes, RemoveAlign) {
+  LLVMContext C;
+  AttrBuilder B;
+  B.addAttribute(Attribute::getWithAlignment(C, 8));
+  AttributeSet AS = AttributeSet::get(C, B);
+  EXPECT_TRUE(AS.getAlignment() == 8);
+  AS = AS.removeAttribute(C, Attribute::Alignment);
+  EXPECT_TRUE(AS.getAlignment() == 0);
+  AttributeList AL;
+  AL = AL.addParamAttributes(C, 0, B);
+  EXPECT_TRUE(AL.hasParamAttrs(0));
+  EXPECT_TRUE(AL.hasParamAttr(0, Attribute::Alignment));
+  EXPECT_TRUE(AL.getParamAlignment(0) == 8);
+  AL = AL.removeParamAttribute(C, 0, Attribute::Alignment);
+  EXPECT_FALSE(AL.hasParamAttr(0, Attribute::Alignment));
+}
+
 TEST(Attributes, AddMatchingAlignAttr) {
   LLVMContext C;
   AttributeList AL;