diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 3c0355a1c39..66e7d9ff50e 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -1556,6 +1556,8 @@ merge_default_template_args (tree new_parms, tree old_parms, bool class_p)
       tree old_parm = TREE_VALUE (TREE_VEC_ELT (old_parms, i));
       tree& new_default = TREE_PURPOSE (TREE_VEC_ELT (new_parms, i));
       tree& old_default = TREE_PURPOSE (TREE_VEC_ELT (old_parms, i));
+      if (error_operand_p (new_parm) || error_operand_p (old_parm))
+	return false;
       if (new_default != NULL_TREE && old_default != NULL_TREE)
 	{
 	  auto_diagnostic_group d;
diff --git a/gcc/testsuite/g++.dg/template/pr108206.C b/gcc/testsuite/g++.dg/template/pr108206.C
new file mode 100644
index 00000000000..9362d261bea
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/pr108206.C
@@ -0,0 +1,5 @@
+// PR c++/108206
+// { dg-do compile { target c++11 } }
+
+template <X x, typename T1> void foo (T1);	// { dg-error "'X' has not been declared" }
+template <X x, typename T2> void foo (T2);	// { dg-error "'X' has not been declared" }