diff --git a/gcc/rust/typecheck/rust-tyty-subst.h b/gcc/rust/typecheck/rust-tyty-subst.h
index b8e928d60f0..3f0b912fa7b 100644
--- a/gcc/rust/typecheck/rust-tyty-subst.h
+++ b/gcc/rust/typecheck/rust-tyty-subst.h
@@ -125,7 +125,7 @@ public:
 				     std::vector<Region> subst)
   {
     RegionParamList list (num_regions);
-    for (size_t i = 0; i < subst.size (); i++)
+    for (size_t i = 0; i < MIN (num_regions, subst.size ()); i++)
       list.regions.at (i) = subst.at (i);
     for (size_t i = subst.size (); i < num_regions; i++)
       {
diff --git a/gcc/testsuite/rust/compile/issue-3605.rs b/gcc/testsuite/rust/compile/issue-3605.rs
new file mode 100644
index 00000000000..05e6e48e66e
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-3605.rs
@@ -0,0 +1,5 @@
+enum Foo<'a> {}
+
+enum Bar<'a> {
+    in_band_def_explicit_impl(Foo<'a>),
+}