diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 5e30a4a907a..751ac61b25a 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -3796,6 +3796,9 @@ diagnose_trait_expr (tree expr, tree args)
     case CPTK_IS_TRIVIALLY_COPYABLE:
       inform (loc, "  %qT is not trivially copyable", t1);
       break;
+    case CPTK_IS_UNBOUNDED_ARRAY:
+      inform (loc, "  %qT is not an unbounded array", t1);
+      break;
     case CPTK_IS_UNION:
       inform (loc, "  %qT is not a union", t1);
       break;
diff --git a/gcc/cp/cp-trait.def b/gcc/cp/cp-trait.def
index 99bc05360b9..4e02f68e4a9 100644
--- a/gcc/cp/cp-trait.def
+++ b/gcc/cp/cp-trait.def
@@ -83,6 +83,7 @@ DEFTRAIT_EXPR (IS_TRIVIAL, "__is_trivial", 1)
 DEFTRAIT_EXPR (IS_TRIVIALLY_ASSIGNABLE, "__is_trivially_assignable", 2)
 DEFTRAIT_EXPR (IS_TRIVIALLY_CONSTRUCTIBLE, "__is_trivially_constructible", -1)
 DEFTRAIT_EXPR (IS_TRIVIALLY_COPYABLE, "__is_trivially_copyable", 1)
+DEFTRAIT_EXPR (IS_UNBOUNDED_ARRAY, "__is_unbounded_array", 1)
 DEFTRAIT_EXPR (IS_UNION, "__is_union", 1)
 DEFTRAIT_EXPR (IS_VOLATILE, "__is_volatile", 1)
 DEFTRAIT_EXPR (REF_CONSTRUCTS_FROM_TEMPORARY, "__reference_constructs_from_temporary", 2)
diff --git a/gcc/cp/cp-trait.gperf b/gcc/cp/cp-trait.gperf
index fb162cac164..a894fc8c74c 100644
--- a/gcc/cp/cp-trait.gperf
+++ b/gcc/cp/cp-trait.gperf
@@ -63,6 +63,7 @@ struct cp_trait {
 "__is_trivially_assignable", CPTK_IS_TRIVIALLY_ASSIGNABLE, 2, false
 "__is_trivially_constructible", CPTK_IS_TRIVIALLY_CONSTRUCTIBLE, -1, false
 "__is_trivially_copyable", CPTK_IS_TRIVIALLY_COPYABLE, 1, false
+"__is_unbounded_array", CPTK_IS_UNBOUNDED_ARRAY, 1, false
 "__is_union", CPTK_IS_UNION, 1, false
 "__is_volatile", CPTK_IS_VOLATILE, 1, false
 "__reference_constructs_from_temporary", CPTK_REF_CONSTRUCTS_FROM_TEMPORARY, 2, false
diff --git a/gcc/cp/cp-trait.h b/gcc/cp/cp-trait.h
index 526e63dec42..47060ffbbef 100644
--- a/gcc/cp/cp-trait.h
+++ b/gcc/cp/cp-trait.h
@@ -116,7 +116,7 @@ cp_trait_lookup::find (const char *str, size_t len)
 {
   enum
     {
-      TOTAL_KEYWORDS = 48,
+      TOTAL_KEYWORDS = 49,
       MIN_WORD_LENGTH = 7,
       MAX_WORD_LENGTH = 37,
       MIN_HASH_VALUE = 7,
@@ -125,30 +125,32 @@ cp_trait_lookup::find (const char *str, size_t len)
 
   static const struct cp_trait wordlist[] =
     {
-#line 76 "../../gcc/cp/cp-trait.gperf"
+#line 77 "../../gcc/cp/cp-trait.gperf"
       {"__bases", CPTK_BASES, 1, true},
 #line 50 "../../gcc/cp/cp-trait.gperf"
       {"__is_enum", CPTK_IS_ENUM, 1, false},
-#line 66 "../../gcc/cp/cp-trait.gperf"
+#line 67 "../../gcc/cp/cp-trait.gperf"
       {"__is_union", CPTK_IS_UNION, 1, false},
-#line 70 "../../gcc/cp/cp-trait.gperf"
-      {"__remove_cv", CPTK_REMOVE_CV, 1, true},
 #line 71 "../../gcc/cp/cp-trait.gperf"
+      {"__remove_cv", CPTK_REMOVE_CV, 1, true},
+#line 72 "../../gcc/cp/cp-trait.gperf"
       {"__remove_cvref", CPTK_REMOVE_CVREF, 1, true},
 #line 49 "../../gcc/cp/cp-trait.gperf"
       {"__is_empty", CPTK_IS_EMPTY, 1, false},
 #line 62 "../../gcc/cp/cp-trait.gperf"
       {"__is_trivial", CPTK_IS_TRIVIAL, 1, false},
-#line 72 "../../gcc/cp/cp-trait.gperf"
+#line 73 "../../gcc/cp/cp-trait.gperf"
       {"__remove_reference", CPTK_REMOVE_REFERENCE, 1, true},
-#line 77 "../../gcc/cp/cp-trait.gperf"
+#line 78 "../../gcc/cp/cp-trait.gperf"
       {"__direct_bases", CPTK_DIRECT_BASES, 1, true},
-#line 74 "../../gcc/cp/cp-trait.gperf"
+#line 75 "../../gcc/cp/cp-trait.gperf"
       {"__underlying_type", CPTK_UNDERLYING_TYPE, 1, true},
-#line 67 "../../gcc/cp/cp-trait.gperf"
+#line 68 "../../gcc/cp/cp-trait.gperf"
       {"__is_volatile", CPTK_IS_VOLATILE, 1, false},
-#line 73 "../../gcc/cp/cp-trait.gperf"
+#line 74 "../../gcc/cp/cp-trait.gperf"
       {"__type_pack_element", CPTK_TYPE_PACK_ELEMENT, -1, true},
+#line 66 "../../gcc/cp/cp-trait.gperf"
+      {"__is_unbounded_array", CPTK_IS_UNBOUNDED_ARRAY, 1, false},
 #line 59 "../../gcc/cp/cp-trait.gperf"
       {"__is_polymorphic", CPTK_IS_POLYMORPHIC, 1, false},
 #line 53 "../../gcc/cp/cp-trait.gperf"
@@ -161,9 +163,9 @@ cp_trait_lookup::find (const char *str, size_t len)
       {"__is_layout_compatible", CPTK_IS_LAYOUT_COMPATIBLE, 2, false},
 #line 64 "../../gcc/cp/cp-trait.gperf"
       {"__is_trivially_constructible", CPTK_IS_TRIVIALLY_CONSTRUCTIBLE, -1, false},
-#line 69 "../../gcc/cp/cp-trait.gperf"
+#line 70 "../../gcc/cp/cp-trait.gperf"
       {"__reference_converts_from_temporary", CPTK_REF_CONVERTS_FROM_TEMPORARY, 2, false},
-#line 68 "../../gcc/cp/cp-trait.gperf"
+#line 69 "../../gcc/cp/cp-trait.gperf"
       {"__reference_constructs_from_temporary", CPTK_REF_CONSTRUCTS_FROM_TEMPORARY, 2, false},
 #line 33 "../../gcc/cp/cp-trait.gperf"
       {"__has_nothrow_copy", CPTK_HAS_NOTHROW_COPY, 1, false},
@@ -219,21 +221,21 @@ cp_trait_lookup::find (const char *str, size_t len)
       {"__is_assignable", CPTK_IS_ASSIGNABLE, 2, false},
 #line 61 "../../gcc/cp/cp-trait.gperf"
       {"__is_standard_layout", CPTK_IS_STD_LAYOUT, 1, false},
-#line 75 "../../gcc/cp/cp-trait.gperf"
+#line 76 "../../gcc/cp/cp-trait.gperf"
       {"__is_deducible ", CPTK_IS_DEDUCIBLE, 2, false}
     };
 
   static const signed char lookup[] =
     {
       -1, -1, -1, -1, -1, -1, -1,  0, -1,  1,  2,  3, -1, -1,
-       4,  5, -1,  6,  7,  8, -1, -1,  9, 10, 11, -1, 12, 13,
-      14, -1, 15, -1, 16, 17, -1, 18, -1, 19, 20, -1, 21, -1,
-      22, -1, 23, 24, -1, 25, 26, 27, 28, -1, 29, -1, 30, 31,
-      -1, -1, 32, 33, 34, 35, -1, 36, 37, 38, 39, -1, 40, -1,
-      41, -1, -1, -1, -1, 42, -1, -1, -1, -1, -1, -1, -1, -1,
-      -1, 43, -1, -1, 44, -1, 45, -1, -1, -1, -1, 46, -1, -1,
+       4,  5, -1,  6,  7,  8, -1, -1,  9, 10, 11, 12, 13, 14,
+      15, -1, 16, -1, 17, 18, -1, 19, -1, 20, 21, -1, 22, -1,
+      23, -1, 24, 25, -1, 26, 27, 28, 29, -1, 30, -1, 31, 32,
+      -1, -1, 33, 34, 35, 36, -1, 37, 38, 39, 40, -1, 41, -1,
+      42, -1, -1, -1, -1, 43, -1, -1, -1, -1, -1, -1, -1, -1,
+      -1, 44, -1, -1, 45, -1, 46, -1, -1, -1, -1, 47, -1, -1,
       -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-      -1, -1, -1, 47
+      -1, -1, -1, 48
     };
 
   if (len <= MAX_WORD_LENGTH && len >= MIN_WORD_LENGTH)
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index e1358afcb3f..0a2699be476 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -12217,6 +12217,9 @@ trait_expr_value (cp_trait_kind kind, tree type1, tree type2)
     case CPTK_IS_TRIVIALLY_COPYABLE:
       return trivially_copyable_p (type1);
 
+    case CPTK_IS_UNBOUNDED_ARRAY:
+      return array_of_unknown_bound_p (type1);
+
     case CPTK_IS_UNION:
       return type_code1 == UNION_TYPE;
 
@@ -12384,6 +12387,7 @@ finish_trait_expr (location_t loc, cp_trait_kind kind, tree type1, tree type2)
     case CPTK_IS_CONST:
     case CPTK_IS_ENUM:
     case CPTK_IS_SAME:
+    case CPTK_IS_UNBOUNDED_ARRAY:
     case CPTK_IS_UNION:
     case CPTK_IS_VOLATILE:
       break;
diff --git a/gcc/testsuite/g++.dg/ext/has-builtin-1.C b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
index 645cabe088e..90997210c12 100644
--- a/gcc/testsuite/g++.dg/ext/has-builtin-1.C
+++ b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
@@ -131,6 +131,9 @@
 #if !__has_builtin (__is_trivially_copyable)
 # error "__has_builtin (__is_trivially_copyable) failed"
 #endif
+#if !__has_builtin (__is_unbounded_array)
+# error "__has_builtin (__is_unbounded_array) failed"
+#endif
 #if !__has_builtin (__is_union)
 # error "__has_builtin (__is_union) failed"
 #endif
diff --git a/gcc/testsuite/g++.dg/ext/is_unbounded_array.C b/gcc/testsuite/g++.dg/ext/is_unbounded_array.C
new file mode 100644
index 00000000000..1307d24f5a5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_unbounded_array.C
@@ -0,0 +1,37 @@
+// { dg-do compile { target c++11 } }
+
+#include <testsuite_tr1.h>
+
+using namespace __gnu_test;
+
+#define SA(X) static_assert((X),#X)
+
+#define SA_TEST_CATEGORY(TRAIT, TYPE, EXPECT)	\
+  SA(TRAIT(TYPE) == EXPECT);					\
+  SA(TRAIT(const TYPE) == EXPECT);				\
+  SA(TRAIT(volatile TYPE) == EXPECT);			\
+  SA(TRAIT(const volatile TYPE) == EXPECT)
+
+SA_TEST_CATEGORY(__is_unbounded_array, int[2], false);
+SA_TEST_CATEGORY(__is_unbounded_array, int[], true);
+SA_TEST_CATEGORY(__is_unbounded_array, int[2][3], false);
+SA_TEST_CATEGORY(__is_unbounded_array, int[][3], true);
+SA_TEST_CATEGORY(__is_unbounded_array, float*[2], false);
+SA_TEST_CATEGORY(__is_unbounded_array, float*[], true);
+SA_TEST_CATEGORY(__is_unbounded_array, float*[2][3], false);
+SA_TEST_CATEGORY(__is_unbounded_array, float*[][3], true);
+SA_TEST_CATEGORY(__is_unbounded_array, ClassType[2], false);
+SA_TEST_CATEGORY(__is_unbounded_array, ClassType[], true);
+SA_TEST_CATEGORY(__is_unbounded_array, ClassType[2][3], false);
+SA_TEST_CATEGORY(__is_unbounded_array, ClassType[][3], true);
+SA_TEST_CATEGORY(__is_unbounded_array, IncompleteClass[2][3], false);
+SA_TEST_CATEGORY(__is_unbounded_array, IncompleteClass[][3], true);
+SA_TEST_CATEGORY(__is_unbounded_array, int(*)[2], false);
+SA_TEST_CATEGORY(__is_unbounded_array, int(*)[], false);
+SA_TEST_CATEGORY(__is_unbounded_array, int(&)[2], false);
+SA_TEST_CATEGORY(__is_unbounded_array, int(&)[], false);
+
+// Sanity check.
+SA_TEST_CATEGORY(__is_unbounded_array, ClassType, false);
+SA_TEST_CATEGORY(__is_unbounded_array, IncompleteClass, false);
+SA_TEST_CATEGORY(__is_unbounded_array, IncompleteUnion, false);
