diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index c0a37a51cba3c815c49460e36394795fdcdad96c..c9219d5b3a5ae0fe0e5ba723a96d8c0526820973 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -13480,7 +13480,12 @@ extract_locals_r (tree *tp, int *walk_subtrees, void *data_)
        outermost tree.  Nested *_EXTRA_ARGS should naturally be empty since
        the outermost (extra-args) tree will intercept any substitution before
        a nested tree can.  */
-    gcc_checking_assert (tree_extra_args (*tp) == NULL_TREE);
+    gcc_checking_assert (tree_extra_args (*tp) == NULL_TREE
+			/* Except a lambda nested inside an extra-args tree
+			   can have extra args if we deferred partial
+			   substitution into it at template parse time.  But
+			   we don't walk LAMBDA_EXPR_EXTRA_ARGS anyway.  */
+			 || TREE_CODE (*tp) == LAMBDA_EXPR);
 
   if (TREE_CODE (*tp) == DECL_EXPR)
     {
diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-targ9.C b/gcc/testsuite/g++.dg/cpp2a/lambda-targ9.C
new file mode 100644
index 0000000000000000000000000000000000000000..41f8526184a8a9903f181b7800bdc7dfc6eea608
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/lambda-targ9.C
@@ -0,0 +1,16 @@
+// PR c++/117054
+// { dg-do compile { target c++20 } }
+
+template<auto = []{}>
+constexpr bool v = true;
+
+template<typename>
+void f() {
+  [](auto) {
+    if constexpr (v<>) { }
+  }(0);
+}
+
+int main() {
+  f<int>();
+}