diff --git a/llvm/include/llvm/Demangle/RustDemangle.h b/llvm/include/llvm/Demangle/RustDemangle.h
--- a/llvm/include/llvm/Demangle/RustDemangle.h
+++ b/llvm/include/llvm/Demangle/RustDemangle.h
@@ -12,12 +12,14 @@
 #include "llvm/Demangle/DemangleConfig.h"
 #include "llvm/Demangle/StringView.h"
 #include "llvm/Demangle/Utility.h"
+#include <cstdint>
 
 namespace llvm {
 namespace rust_demangle {
 
 using llvm::itanium_demangle::OutputStream;
 using llvm::itanium_demangle::StringView;
+using llvm::itanium_demangle::SwapAndRestore;
 
 struct Identifier {
   StringView Name;
@@ -52,10 +54,17 @@
   void demanglePath();
 
   Identifier parseIdentifier();
-  void parseOptionalBase62Number(char Tag);
+  uint64_t parseOptionalBase62Number(char Tag);
   uint64_t parseBase62Number();
   uint64_t parseDecimalNumber();
 
+  void print(char C) {
+    if (Error)
+      return;
+
+    Output += C;
+  }
+
   void print(StringView S) {
     if (Error)
       return;
@@ -63,6 +72,13 @@
     Output += S;
   }
 
+  void printDecimalNumber(uint64_t N) {
+    if (Error)
+      return;
+
+    Output << N;
+  }
+
   char look() const {
     if (Error || Position >= Input.size())
       return 0;
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
@@ -132,7 +132,7 @@
     Error = true;
     return;
   }
-  RecursionLevel += 1;
+  SwapAndRestore<size_t> SaveRecursionLevel(RecursionLevel, RecursionLevel + 1);
 
   switch (consume()) {
   case 'C': {
@@ -149,15 +149,31 @@
     }
     demanglePath();
 
-    parseOptionalBase62Number('s');
+    uint64_t Disambiguator = parseOptionalBase62Number('s');
     Identifier Ident = parseIdentifier();
 
-    if (!Ident.empty()) {
-      // FIXME print special namespaces:
-      // * "C" closures
-      // * "S" shim
-      print("::");
-      print(Ident.Name);
+    if (isUpper(NS)) {
+      // Special namespaces
+      print("::{");
+      if (NS == 'C')
+        print("closure");
+      else if (NS == 'S')
+        print("shim");
+      else
+        print(NS);
+      if (!Ident.empty()) {
+        print(":");
+        print(Ident.Name);
+      }
+      print('#');
+      printDecimalNumber(Disambiguator);
+      print('}');
+    } else {
+      // Implementation internal namespaces.
+      if (!Ident.empty()) {
+        print("::");
+        print(Ident.Name);
+      }
     }
     break;
   }
@@ -166,8 +182,6 @@
     Error = true;
     break;
   }
-
-  RecursionLevel -= 1;
 }
 
 // <undisambiguated-identifier> = ["u"] <decimal-number> ["_"] <bytes>
@@ -195,11 +209,16 @@
 }
 
 // Parses optional base 62 number. The presence of a number is determined using
-// Tag.
-void Demangler::parseOptionalBase62Number(char Tag) {
-  // Parsing result is currently unused.
-  if (consumeIf(Tag))
-    parseBase62Number();
+// Tag. Returns 0 when tag is absent and parsed value + 1 otherwise.
+uint64_t Demangler::parseOptionalBase62Number(char Tag) {
+  if (!consumeIf(Tag))
+    return 0;
+
+  uint64_t N = parseBase62Number();
+  if (Error || !addAssign(N, 1))
+    return 0;
+
+  return N;
 }
 
 // Parses base 62 number with <0-9a-zA-Z> as digits. Number is terminated by
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
@@ -9,6 +9,30 @@
 CHECK: a::b::c
        _RNvNvC1a1b1c
 
+; Closure namespace
+
+CHECK: crate::{closure#0}
+       _RNCC5crate0
+
+CHECK: crate::{closure#1}
+       _RNCC5crates_0
+
+CHECK: crate::{closure:ab#0}
+       _RNCC5crate2ab
+
+CHECK: crate::{closure:ab#1}
+       _RNCC5crates_2ab
+
+; Shim namespace
+
+CHECK: crate::{shim:reify#0}
+       _RNSC5crate5reify
+
+; Unrecognized special namespace
+
+CHECK: a::{B:c#10}
+       _RNBC1as8_1c
+
 ; Invalid mangled characters
 
 CHECK: _RNvC2a.1c
@@ -17,6 +41,11 @@
 CHECK: _RNvC2a$1c
        _RNvC2a$1c
 
+; Invalid namespace (not in [a-zA-Z]).
+
+CHECK: _RN_C1a1b
+       _RN_C1a1b
+
 ; Invalid identifier length (UINT64_MAX + 3, which happens to be ok after a wraparound).
 
 CHECK: _RNvC2ab18446744073709551618xy