diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 244070d93c2..000df847342 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -3861,6 +3861,9 @@ 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 18e2d0f3480..05514a51c21 100644
--- a/gcc/cp/cp-trait.def
+++ b/gcc/cp/cp-trait.def
@@ -92,6 +92,7 @@ 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/semantics.cc b/gcc/cp/semantics.cc
index 9dcdb06191a..1794e83baa2 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -12532,6 +12532,9 @@ 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;
 
@@ -12708,6 +12711,7 @@ finish_trait_expr (location_t loc, cp_trait_kind kind, tree type1, tree type2)
     case CPTK_IS_REFERENCE:
     case CPTK_IS_SAME:
     case CPTK_IS_SCOPED_ENUM:
+    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 96b7a89e4f1..b1430e9bd8b 100644
--- a/gcc/testsuite/g++.dg/ext/has-builtin-1.C
+++ b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
@@ -158,6 +158,9 @@
 #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..283a74e1a0a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_unbounded_array.C
@@ -0,0 +1,37 @@
+// { dg-do compile { target c++11 } }
+
+#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)
+
+class ClassType { };
+class IncompleteClass;
+union IncompleteUnion;
+
+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);
