diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index edab147c78d..3294b4fa943 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -17991,6 +17991,9 @@ require_deduced_type (tree decl, tsubst_flags_t complain)
 tree
 build_explicit_specifier (tree expr, tsubst_flags_t complain)
 {
+  if (check_for_bare_parameter_packs (expr))
+    return error_mark_node;
+
   if (instantiation_dependent_expression_p (expr))
     /* Wait for instantiation, tsubst_function_decl will handle it.  */
     return expr;
diff --git a/gcc/cp/except.c b/gcc/cp/except.c
index 0bbc229490e..cbafc09629b 100644
--- a/gcc/cp/except.c
+++ b/gcc/cp/except.c
@@ -1228,6 +1228,8 @@ type_throw_all_p (const_tree type)
 tree
 build_noexcept_spec (tree expr, tsubst_flags_t complain)
 {
+  if (check_for_bare_parameter_packs (expr))
+    return error_mark_node;
   if (TREE_CODE (expr) != DEFERRED_NOEXCEPT
       && !value_dependent_expression_p (expr))
     {
diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept66.C b/gcc/testsuite/g++.dg/cpp0x/noexcept66.C
new file mode 100644
index 00000000000..6c76d9146ad
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/noexcept66.C
@@ -0,0 +1,13 @@
+// PR c++/99844
+// { dg-do compile { target c++11 } }
+
+template <bool... B>
+struct S {
+ void fn() noexcept(B); // { dg-error "parameter packs not expanded" }
+};
+
+void fn ()
+{
+  S<true> s;
+  s.fn();
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/explicit16.C b/gcc/testsuite/g++.dg/cpp2a/explicit16.C
index 9d95b0d669e..9c20f6332e9 100644
--- a/gcc/testsuite/g++.dg/cpp2a/explicit16.C
+++ b/gcc/testsuite/g++.dg/cpp2a/explicit16.C
@@ -1,5 +1,5 @@
 // PR c++/95066 - explicit malfunction with dependent expression.
-// { dg-do compile { target c++2a } }
+// { dg-do compile { target c++20 } }
 
 template <typename T>
 struct Foo {
diff --git a/gcc/testsuite/g++.dg/cpp2a/explicit17.C b/gcc/testsuite/g++.dg/cpp2a/explicit17.C
new file mode 100644
index 00000000000..38a61f4a273
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/explicit17.C
@@ -0,0 +1,9 @@
+// PR c++/99844
+// { dg-do compile { target c++20 } }
+
+template <bool... B>
+struct S {
+  constexpr explicit(B) S() {} // { dg-error "parameter packs not expanded" }
+};
+
+constexpr S<true> s;