diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -16072,7 +16072,7 @@
 
     DiagRuntimeBehavior(BaseExpr->getBeginLoc(), BaseExpr,
                         PDiag(DiagID) << toString(index, 10, true)
-                                      << toString(size, 10, true)
+                                      << toString(ArrayTy->getSize(), 10, true)
                                       << (unsigned)size.getLimitedValue(~0U)
                                       << IndexExpr->getSourceRange());
   } else {
diff --git a/clang/test/Sema/array-bounds-ptr-arith.c b/clang/test/Sema/array-bounds-ptr-arith.c
--- a/clang/test/Sema/array-bounds-ptr-arith.c
+++ b/clang/test/Sema/array-bounds-ptr-arith.c
@@ -11,7 +11,7 @@
   return (void *)es->s_uuid + sizeof(int); // no-warning
 }
 void* broken (struct ext2_super_block *es,int a) {
-  return (void *)es->s_uuid + 9; // expected-warning {{the pointer incremented by 9 refers past the end of the array}}
+  return (void *)es->s_uuid + 9; // expected-warning {{the pointer incremented by 9 refers past the end of the array (that contains 8 elements)}}
 }
 
 // Test case reduced from PR11594
diff --git a/clang/test/SemaCXX/array-bounds.cpp b/clang/test/SemaCXX/array-bounds.cpp
--- a/clang/test/SemaCXX/array-bounds.cpp
+++ b/clang/test/SemaCXX/array-bounds.cpp
@@ -237,7 +237,7 @@
     ((char*)foo)[sizeof(foo) - 1] = '\0';  // no-warning
     *(((char*)foo) + sizeof(foo) - 1) = '\0';  // no-warning
 
-    ((char*)foo)[sizeof(foo)] = '\0';  // expected-warning {{array index 32768 is past the end of the array (which contains 32768 elements)}}
+    ((char*)foo)[sizeof(foo)] = '\0';  // expected-warning {{array index 32768 is past the end of the array (which contains 4096 elements)}}
 
     // TODO: This should probably warn, too.
     *(((char*)foo) + sizeof(foo)) = '\0';  // no-warning