Index: lib/Sema/SemaType.cpp
===================================================================
--- lib/Sema/SemaType.cpp
+++ lib/Sema/SemaType.cpp
@@ -1396,6 +1396,14 @@
                                            S.LangOpts.GNUMode).isInvalid();
 }
 
+/// Set NumElements to the max size that an array of ElementType can be,
+/// using MaxBits addressing.
+static void getMaxArraySize(ASTContext &Context, QualType ElementType,
+                            unsigned MaxBits, llvm::APSInt &NumElements) {
+  uint64_t ElementSize = Context.getTypeSizeInChars(ElementType).getQuantity();
+  llvm::APInt ElementSizeInt(MaxBits, ElementSize);
+  NumElements = llvm::APInt::getAllOnesValue(MaxBits).udiv(ElementSizeInt);
+}
 
 /// \brief Build an array type.
 ///
@@ -1549,10 +1557,14 @@
       // Is the array too large?
       unsigned ActiveSizeBits
         = ConstantArrayType::getNumAddressingBits(Context, T, ConstVal);
-      if (ActiveSizeBits > ConstantArrayType::getMaxSizeBits(Context))
+      if (ActiveSizeBits > ConstantArrayType::getMaxSizeBits(Context)) {
         Diag(ArraySize->getLocStart(), diag::err_array_too_large)
           << ConstVal.toString(10)
           << ArraySize->getSourceRange();
+        // Set array size to largest allowable size.
+        getMaxArraySize(Context, T, ConstantArrayType::getMaxSizeBits(Context),
+                        ConstVal);
+      }
     }
 
     T = Context.getConstantArrayType(T, ConstVal, ASM, Quals);
Index: test/Sema/offsetof-64.c
===================================================================
--- test/Sema/offsetof-64.c
+++ test/Sema/offsetof-64.c
@@ -1,15 +1,20 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s -triple x86_64-linux-gnu
-// expected-no-diagnostics
 
 // PR15216
 // Don't crash when taking computing the offset of structs with large arrays.
 const unsigned long Size = (1l << 62);
 
-struct Chunk {
+struct Chunk1 {
   char padding[Size];
   char more_padding[1][Size];
   char data;
 };
 
-int test1 = __builtin_offsetof(struct Chunk, data);
+int test1 = __builtin_offsetof(struct Chunk1, data);
 
+struct Chunk2 {
+  char padding[Size][Size][Size];  // expected-error 2{{array is too large}}
+  char data;
+};
+
+int test2 = __builtin_offsetof(struct Chunk2, data);