diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 00804a7eea15..c17870039ed2 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -8017,6 +8017,18 @@ convert_nontype_argument (tree type, tree expr, tsubst_flags_t complain)
 		   "because it is of type %qT", expr, type, TREE_TYPE (expr));
 	  return NULL_TREE;
 	}
+      if (!integer_zerop (expr) && !val_dep_p)
+	{
+	  if (complain & tf_error)
+	    {
+	      expr = cxx_constant_value (expr);
+	      if (expr == error_mark_node)
+		return NULL_TREE;
+	      gcc_assert (integer_zerop (expr));
+	    }
+	  else
+	    return NULL_TREE;
+	}
       return expr;
     }
   else if (CLASS_TYPE_P (type))
@@ -8037,6 +8049,18 @@ convert_nontype_argument (tree type, tree expr, tsubst_flags_t complain)
 		   "because it is of type %qT", expr, type, TREE_TYPE (expr));
 	  return NULL_TREE;
 	}
+      if (!REFLECT_EXPR_P (expr) && !val_dep_p)
+	{
+	  if (complain & tf_error)
+	    {
+	      expr = cxx_constant_value (expr);
+	      if (expr == error_mark_node)
+		return NULL_TREE;
+	      gcc_assert (REFLECT_EXPR_P (expr));
+	    }
+	  else
+	    return NULL_TREE;
+	}
       return expr;
     }
   /* A template non-type parameter must be one of the above.  */
diff --git a/gcc/testsuite/g++.dg/cpp26/pr124070.C b/gcc/testsuite/g++.dg/cpp26/pr124070.C
new file mode 100644
index 000000000000..4721c0ff2154
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp26/pr124070.C
@@ -0,0 +1,20 @@
+// PR c++/124070
+// { dg-do compile { target c++26 } }
+
+constexpr decltype (nullptr)
+bar (bool x)
+{
+  if (x)
+    throw 1;
+  return nullptr;
+}
+
+template <decltype (nullptr) I = bar (true)>	// { dg-error "uncaught exception '1'" }
+constexpr void
+foo ()
+{
+}
+
+consteval {
+  foo <> ();					// { dg-error "no matching function for call to 'foo<>\\\(\\\)'" }
+}
diff --git a/gcc/testsuite/g++.dg/reflect/define_aggregate7.C b/gcc/testsuite/g++.dg/reflect/define_aggregate7.C
new file mode 100644
index 000000000000..2ea8f86f35e2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/reflect/define_aggregate7.C
@@ -0,0 +1,13 @@
+// PR c++/124070
+// { dg-do compile { target c++26 } }
+// { dg-additional-options "-freflection" }
+
+#include <meta>
+
+struct S;
+template <std::meta::info I = define_aggregate (^^S, {})>	// { dg-error "'define_aggregate' not evaluated from 'consteval' block" }
+constexpr void foo () {}
+
+consteval {
+  foo <> ();	// { dg-error "no matching function for call to 'foo<>\\\(\\\)'" }
+}
diff --git a/gcc/testsuite/g++.dg/reflect/define_aggregate8.C b/gcc/testsuite/g++.dg/reflect/define_aggregate8.C
new file mode 100644
index 000000000000..55372d2e3cad
--- /dev/null
+++ b/gcc/testsuite/g++.dg/reflect/define_aggregate8.C
@@ -0,0 +1,12 @@
+// PR c++/124070
+// { dg-do compile { target c++26 } }
+// { dg-additional-options "-freflection" }
+
+#include <meta>
+
+struct S;
+consteval void bar (std::meta::info a = define_aggregate (^^S, {})) {}
+consteval {
+  bar ();
+}
+S s;
diff --git a/gcc/testsuite/g++.dg/reflect/parameters_of4.C b/gcc/testsuite/g++.dg/reflect/parameters_of4.C
index a5b4230db770..fe646e2f253f 100644
--- a/gcc/testsuite/g++.dg/reflect/parameters_of4.C
+++ b/gcc/testsuite/g++.dg/reflect/parameters_of4.C
@@ -4,9 +4,10 @@
 
 #include <meta>
 
-template<auto R> void foo () {}  // { dg-message "sorry, unimplemented: mangling" }
+template<auto R> void foo () {}
 void
 g ()
 {
-  foo<std::meta::parameters_of(^^g)[0]>();
+  foo<std::meta::parameters_of(^^g)[0]>();	// { dg-error "no matching function for call to" }
 }
+// { dg-error "call to non-'constexpr' function" "" { target *-*-* } 0 }