diff --git a/llvm/lib/Demangle/RustDemangle.cpp b/llvm/lib/Demangle/RustDemangle.cpp
--- a/llvm/lib/Demangle/RustDemangle.cpp
+++ b/llvm/lib/Demangle/RustDemangle.cpp
@@ -438,8 +438,13 @@
 //          | "D" <dyn-bounds> <lifetime> // dyn Trait<Assoc = X> + Send + 'a
 //          | <backref>                   // backref
 void Demangler::demangleType() {
-  size_t Start = Position;
+  if (Error || RecursionLevel >= MaxRecursionLevel) {
+    Error = true;
+    return;
+  }
+  SwapAndRestore<size_t> SaveRecursionLevel(RecursionLevel, RecursionLevel + 1);
 
+  size_t Start = Position;
   char C = consume();
   BasicType Type;
   if (parseBasicType(C, Type))
@@ -506,6 +511,9 @@
       Error = true;
     }
     break;
+  case 'B':
+    demangleBackref([&] { demangleType(); });
+    break;
   default:
     Position = Start;
     demanglePath(rust_demangle::InType::Yes);
diff --git a/llvm/test/Demangle/rust.test b/llvm/test/Demangle/rust.test
--- a/llvm/test/Demangle/rust.test
+++ b/llvm/test/Demangle/rust.test
@@ -425,6 +425,9 @@
 CHECK: backref::<backref::ident>
        _RIC7backrefNvB0_5identE
 
+CHECK: backref::<(), ()>
+       _RIC7backrefuB9_E
+
 ; Invalid backreferences
 
 CHECK: _RB_
@@ -436,6 +439,9 @@
 CHECK: _RNvB_1a
        _RNvB_1a
 
+CHECK: _RIC7backrefSB9_E
+       _RIC7backrefSB9_E
+
 ; Invalid mangled characters
 
 CHECK: _RNvC2a.1c