Index: testsuite/g++.dg/concepts/fn-concept2.C
===================================================================
--- testsuite/g++.dg/concepts/fn-concept2.C	(revision 0)
+++ testsuite/g++.dg/concepts/fn-concept2.C	(revision 0)
@@ -0,0 +1,7 @@
+// { dg-options "-std=c++1z" }
+
+template<typename T>
+  concept auto C1() { return 0; } // { dg-error "deduced return type" }
+
+template<typename T>
+  concept int C2() { return 0; } // { dg-error "return type" }
Index: cp/constraint.cc
===================================================================
--- cp/constraint.cc	(revision 215718)
+++ cp/constraint.cc	(working copy)
@@ -280,11 +280,6 @@ check_function_concept (tree fn)
 {
   location_t loc = DECL_SOURCE_LOCATION (fn);
 
-  // If fn was declared with auto, make sure the result type is bool.
-  if (FNDECL_USED_AUTO (fn) && TREE_TYPE (fn) != boolean_type_node) 
-    error_at (loc, "deduced type of concept definition %qD is %qT and not %qT", 
-              fn, TREE_TYPE (fn), boolean_type_node);
-
   // Check that the function is comprised of only a single
   // return statement.
   tree body = DECL_SAVED_TREE (fn);
Index: cp/decl.c
===================================================================
--- cp/decl.c	(revision 215718)
+++ cp/decl.c	(working copy)
@@ -7525,9 +7525,13 @@ check_concept_fn (tree fn)
   if (DECL_ARGUMENTS (fn))
     error ("concept %q#D declared with function parameters", fn);
 
-  // The result type must be convertible to bool.
-  if (!same_type_p (TREE_TYPE (TREE_TYPE (fn)), boolean_type_node))
-    error ("concept %q#D result must be bool", fn);
+  // The declared return type of the concept shall be bool, and
+  // it shall not be deduced from it definition.
+  tree type = TREE_TYPE (TREE_TYPE (fn));
+  if (is_auto (type))
+    error ("concept %q#D declared with a deduced return type", fn);
+  else if (type != boolean_type_node)
+    error ("concept %q#D with return type %qT", fn, type);
 }
 
 /* Helper function.  Replace the temporary this parameter injected