diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 5cdb59d174e..99a7e7247ce 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -3750,6 +3750,9 @@ diagnose_trait_expr (tree expr, tree args)
     case CPTK_IS_FINAL:
       inform (loc, "  %qT is not a final class", t1);
       break;
+    case CPTK_IS_FUNCTION:
+      inform (loc, "  %qT is not a function", t1);
+      break;
     case CPTK_IS_LAYOUT_COMPATIBLE:
       inform (loc, "  %qT is not layout compatible with %qT", t1, t2);
       break;
diff --git a/gcc/cp/cp-trait.def b/gcc/cp/cp-trait.def
index ac9fa026b4e..3bb33a3d5c0 100644
--- a/gcc/cp/cp-trait.def
+++ b/gcc/cp/cp-trait.def
@@ -70,6 +70,7 @@ DEFTRAIT_EXPR (IS_CONVERTIBLE, "__is_convertible", 2)
 DEFTRAIT_EXPR (IS_EMPTY, "__is_empty", 1)
 DEFTRAIT_EXPR (IS_ENUM, "__is_enum", 1)
 DEFTRAIT_EXPR (IS_FINAL, "__is_final", 1)
+DEFTRAIT_EXPR (IS_FUNCTION, "__is_function", 1)
 DEFTRAIT_EXPR (IS_LAYOUT_COMPATIBLE, "__is_layout_compatible", 2)
 DEFTRAIT_EXPR (IS_LITERAL_TYPE, "__is_literal_type", 1)
 DEFTRAIT_EXPR (IS_MEMBER_FUNCTION_POINTER, "__is_member_function_pointer", 1)
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 97ec53a7606..7457475f646 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -12163,6 +12163,9 @@ trait_expr_value (cp_trait_kind kind, tree type1, tree type2)
     case CPTK_IS_FINAL:
       return CLASS_TYPE_P (type1) && CLASSTYPE_FINAL (type1);
 
+    case CPTK_IS_FUNCTION:
+      return type_code1 == FUNCTION_TYPE;
+
     case CPTK_IS_LAYOUT_COMPATIBLE:
       return layout_compatible_type_p (type1, type2);
 
@@ -12390,6 +12393,7 @@ finish_trait_expr (location_t loc, cp_trait_kind kind, tree type1, tree type2)
     case CPTK_IS_CLASS:
     case CPTK_IS_CONST:
     case CPTK_IS_ENUM:
+    case CPTK_IS_FUNCTION:
     case CPTK_IS_MEMBER_FUNCTION_POINTER:
     case CPTK_IS_MEMBER_OBJECT_POINTER:
     case CPTK_IS_MEMBER_POINTER:
diff --git a/gcc/testsuite/g++.dg/ext/has-builtin-1.C b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
index e112d317657..4d3947572a4 100644
--- a/gcc/testsuite/g++.dg/ext/has-builtin-1.C
+++ b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
@@ -89,6 +89,9 @@
 #if !__has_builtin (__is_final)
 # error "__has_builtin (__is_final) failed"
 #endif
+#if !__has_builtin (__is_function)
+# error "__has_builtin (__is_function) failed"
+#endif
 #if !__has_builtin (__is_layout_compatible)
 # error "__has_builtin (__is_layout_compatible) failed"
 #endif
diff --git a/gcc/testsuite/g++.dg/ext/is_function.C b/gcc/testsuite/g++.dg/ext/is_function.C
new file mode 100644
index 00000000000..2e1594b12ad
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_function.C
@@ -0,0 +1,58 @@
+// { 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)
+
+struct A
+{ void fn(); };
+
+template<typename>
+struct AHolder { };
+
+template<class T, class U>
+struct AHolder<U T::*>
+{ using type = U; };
+
+// Positive tests.
+SA(__is_function(int (int)));
+SA(__is_function(ClassType (ClassType)));
+SA(__is_function(float (int, float, int[], int&)));
+SA(__is_function(int (int, ...)));
+SA(__is_function(bool (ClassType) const));
+SA(__is_function(AHolder<decltype(&A::fn)>::type));
+
+void fn();
+SA(__is_function(decltype(fn)));
+
+// Negative tests.
+SA_TEST_CATEGORY(__is_function, int, false);
+SA_TEST_CATEGORY(__is_function, int*, false);
+SA_TEST_CATEGORY(__is_function, int&, false);
+SA_TEST_CATEGORY(__is_function, void, false);
+SA_TEST_CATEGORY(__is_function, void*, false);
+SA_TEST_CATEGORY(__is_function, void**, false);
+SA_TEST_CATEGORY(__is_function, std::nullptr_t, false);
+
+SA_TEST_CATEGORY(__is_function, AbstractClass, false);
+SA(!__is_function(int(&)(int)));
+SA(!__is_function(int(*)(int)));
+
+SA_TEST_CATEGORY(__is_function, A, false);
+SA_TEST_CATEGORY(__is_function, decltype(&A::fn), false);
+
+struct FnCallOverload
+{ void operator()(); };
+SA_TEST_CATEGORY(__is_function, FnCallOverload, false);
+
+// Sanity check.
+SA_TEST_CATEGORY(__is_function, ClassType, false);
+SA_TEST_CATEGORY(__is_function, IncompleteClass, false);
+SA_TEST_CATEGORY(__is_function, IncompleteUnion, false);
