diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 65341c40f97036a034ead6a6b3aba949ed554b4c..c53d8e279c62cf35bc71dd12f44ded5ba3393fe0 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -24148,6 +24148,8 @@ unify_pack_expansion (tree tparms, tree targs, tree packed_parms,
 	     arguments if it is not otherwise deduced.  */
 	  if (cxx_dialect >= cxx20
 	      && TREE_VEC_LENGTH (new_args) < TREE_VEC_LENGTH (old_args)
+	      /* FIXME This isn't set properly for partial instantiations.  */
+	      && TPARMS_PRIMARY_TEMPLATE (tparms)
 	      && builtin_guide_p (TPARMS_PRIMARY_TEMPLATE (tparms)))
 	    TREE_VEC_LENGTH (old_args) = TREE_VEC_LENGTH (new_args);
 	  if (!comp_template_args (old_args, new_args,
diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ78.C b/gcc/testsuite/g++.dg/cpp1y/var-templ78.C
new file mode 100644
index 0000000000000000000000000000000000000000..48366c927751cf782f84fd635ef21fba06bde35c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/var-templ78.C
@@ -0,0 +1,12 @@
+// PR c++/108468
+// { dg-do compile { target c++14 } }
+
+template<int> struct C {
+  template<class, class>
+  static constexpr int x = 1;
+};
+
+template<int I> template<class... A>
+int C<I>::x<void(A...), void(A...)> = 2;
+
+int y = C<0>::x<void(int), void()>;