Index: lib/AST/ASTContext.cpp
===================================================================
--- lib/AST/ASTContext.cpp
+++ lib/AST/ASTContext.cpp
@@ -2496,12 +2496,16 @@
   const Type *TypeNode = Quals.strip(T);
 
   // If this type already has an address space specified, it cannot get
-  // another one.
-  assert(!Quals.hasAddressSpace() &&
-         "Type cannot be in multiple addr spaces!");
-  Quals.addAddressSpace(AddressSpace);
+  // another one. Replace it.
+  if (Quals.hasAddressSpace())
+    Quals.removeAddressSpace();
+  if (AddressSpace != LangAS::Default)
+    Quals.addAddressSpace(AddressSpace);
 
-  return getExtQualType(TypeNode, Quals);
+  if (Quals.hasNonFastQualifiers())
+    return getExtQualType(TypeNode, Quals);
+  else
+    return QualType(TypeNode, Quals.getFastQualifiers());
 }
 
 QualType ASTContext::removeAddrSpaceQualType(QualType T) const {