diff --git a/test/Index/index-templates.cpp b/test/Index/index-templates.cpp
index b79b4be..f550907 100644
--- a/test/Index/index-templates.cpp
+++ b/test/Index/index-templates.cpp
@@ -72,7 +72,7 @@
   swap<T>(x, x);
 }
 
-template<typename T, U>
+template<typename T, typename U>
 struct Pair {
   T first;
   U second;
@@ -85,6 +85,16 @@
   Pair<T, U> p = { t, second_type(u) };
 }
 
+template<typename T>
+struct compare { };
+
+template<typename Key, typename Value, 
+         typename Comparison = compare<Pair<Key, Value> >,
+         typename Allocator = allocator<Pair<Key, Value> > >
+struct map;
+
+void f(map<Z4, Pair<int, Z4> >);
+
 // RUN: c-index-test -test-load-source all %s | FileCheck -check-prefix=CHECK-LOAD %s
 // CHECK-LOAD: index-templates.cpp:4:6: FunctionTemplate=f:4:6 Extent=[3:1 - 4:22]
 // CHECK-LOAD: index-templates.cpp:3:19: TemplateTypeParameter=T:3:19 (Definition) Extent=[3:19 - 3:20]
@@ -154,32 +164,33 @@
 // CHECK-LOAD: index-templates.cpp:71:6: OverloadedDeclRef=f[63:7, 64:9]
 // CHECK-LOAD: index-templates.cpp:72:3: OverloadedDeclRef=swap[58:27, 59:39]
 // CHECK-LOAD: index-templates.cpp:82:6: FunctionTemplate=init_list:82:6 (Definition)
-// CHECK-LOAD: index-templates.cpp:85:14: VarDecl=p:85:14 (Definition) Extent=[85:14 - 85:39]
+// CHECK-LOAD: index-templates.cpp:85:14: VarDecl=p:85:14 (Definition)
 // CHECK-LOAD: index-templates.cpp:85:20: DeclRefExpr=t:82:18 Extent=[85:20 - 85:21]
 // CHECK-LOAD: index-templates.cpp:85:23: TypeRef=second_type:83:13 Extent=[85:23 - 85:34]
 // CHECK-LOAD: index-templates.cpp:85:35: DeclRefExpr=u:82:23 Extent=[85:35 - 85:36]
 
 // RUN: c-index-test -test-load-source-usrs all %s | FileCheck -check-prefix=CHECK-USRS %s
-// CHECK-USRS: index-templates.cpp c:@FT@>3#T#Nt0.0#t>2#T#Nt1.0f#>t0.22t0.0# Extent=[3:1 - 4:22]
+// CHECK-USRS: index-templates.cpp c:@FT@>3#T#Nt0.0#t>2#T#Nt1.0f#>t0.22S0_# Extent=[3:1 - 4:22]
 // CHECK-USRS: index-templates.cpp c:index-templates.cpp@79 Extent=[3:19 - 3:20]
 // CHECK-USRS: index-templates.cpp c:index-templates.cpp@82 Extent=[3:22 - 3:29]
 // CHECK-USRS: index-templates.cpp c:index-templates.cpp@91 Extent=[3:31 - 3:67]
-// CHECK-USRS: index-templates.cpp c:index-templates.cpp@136@FT@>3#T#Nt0.0#t>2#T#Nt1.0f#>t0.22t0.0#@x Extent=[4:8 - 4:21]
+// CHECK-USRS: index-templates.cpp c:index-templates.cpp@136@FT@>3#T#Nt0.0#t>2#T#Nt1.0f#>t0.22S0_#@x Extent=[4:8 - 4:21]
 // CHECK-USRS: index-templates.cpp c:@CT>1#T@allocator Extent=[6:1 - 6:37]
 // CHECK-USRS: index-templates.cpp c:index-templates.cpp@171 Extent=[6:19 - 6:20]
 // CHECK-USRS: index-templates.cpp c:@CT>2#T#T@vector Extent=[8:1 - 11:2]
 // CHECK-USRS: index-templates.cpp c:index-templates.cpp@210 Extent=[8:19 - 8:20]
 // CHECK-USRS: index-templates.cpp c:index-templates.cpp@222 Extent=[8:31 - 8:36]
 // CHECK-USRS: index-templates.cpp c:@CT>2#T#T@vector@F@clear# Extent=[10:8 - 10:15]
-// CHECK-USRS: index-templates.cpp c:index-templates.cpp@280@CP>1#T@vector>#*t0.0#>@CT>1#T@allocator1*t0.0 Extent=[13:1 - 14:21]
+// CHECK-USRS: index-templates.cpp c:index-templates.cpp@280@CP>1#T@vector>#*t0.0#>@CT>1#T@allocator1S0_ Extent=[13:1 - 14:21]
 // CHECK-USRS: index-templates.cpp c:index-templates.cpp@298 Extent=[13:19 - 13:20]
 // CHECK-USRS: index-templates.cpp c:@S@Z1 Extent=[16:1 - 16:14]
-// CHECK-USRS: index-templates.cpp c:@C@vector>#$@S@Z1#$@C@allocator>#$@S@Z1 Extent=[18:1 - 18:22]
+// CHECK-USRS: index-templates.cpp c:@C@vector>#$@S@Z1#$@C@allocator>#S0_ Extent=[18:1 - 18:22]
 // CHECK-USRS: index-templates.cpp c:@S@Z2 Extent=[20:1 - 20:14]
-// CHECK-USRS: index-templates.cpp c:@C@vector>#$@S@Z2#$@C@allocator>#$@S@Z2 Extent=[22:1 - 25:2]
-// CHECK-USRS: index-templates.cpp c:@C@vector>#$@S@Z2#$@C@allocator>#$@S@Z2@F@clear# Extent=[24:8 - 24:15]
+// CHECK-USRS: index-templates.cpp c:@C@vector>#$@S@Z2#$@C@allocator>#S0_ Extent=[22:1 - 25:2]
+// CHECK-USRS: index-templates.cpp c:@C@vector>#$@S@Z2#$@C@allocator>#S0_@F@clear# Extent=[24:8 - 24:15]
 // CHECK-USRS: index-templates.cpp c:@ST>2#T#T@Y Extent=[27:1 - 31:2]
 // CHECK-USRS: index-templates.cpp c:index-templates.cpp@452 Extent=[27:19 - 27:20]
 // CHECK-USRS: index-templates.cpp c:index-templates.cpp@464 Extent=[27:31 - 27:32]
 // CHECK-USRS-NOT: type
 // CHECK-USRS: index-templates.cpp c:@S@Z3 Extent=[33:1 - 33:14]
+// CHECK-USES: index-templates.cpp c:@F@f#$@S@map>#$@S@Z4#$@S@Pair>#I#S1_#$@S@compare>#$@S@Pair>#S1_#S2_#$@C@allocator>#S4_#
diff --git a/tools/libclang/CIndexUSRs.cpp b/tools/libclang/CIndexUSRs.cpp
index 8f3dacf..5541657 100644
--- a/tools/libclang/CIndexUSRs.cpp
+++ b/tools/libclang/CIndexUSRs.cpp
@@ -34,6 +34,9 @@
   bool IgnoreResults;
   ASTUnit *AU;
   bool generatedLoc;
+  
+  llvm::DenseMap<const Type *, unsigned> TypeSubstitutions;
+  
 public:
   USRGenerator(const CXCursor *C = 0)
     : Out(Buf),
@@ -510,32 +513,6 @@
 
     // Mangle in ObjC GC qualifiers?
 
-    if (const PointerType *PT = T->getAs<PointerType>()) {
-      Out << '*';
-      T = PT->getPointeeType();
-      continue;
-    }
-    if (const ReferenceType *RT = T->getAs<ReferenceType>()) {
-      Out << '&';
-      T = RT->getPointeeType();
-      continue;
-    }
-    if (const FunctionProtoType *FT = T->getAs<FunctionProtoType>()) {
-      Out << 'F';
-      VisitType(FT->getResultType());
-      for (FunctionProtoType::arg_type_iterator
-            I = FT->arg_type_begin(), E = FT->arg_type_end(); I!=E; ++I) {
-        VisitType(*I);
-      }
-      if (FT->isVariadic())
-        Out << '.';
-      return;
-    }
-    if (const BlockPointerType *BT = T->getAs<BlockPointerType>()) {
-      Out << 'B';
-      T = BT->getPointeeType();
-      continue;
-    }
     if (const BuiltinType *BT = T->getAs<BuiltinType>()) {
       unsigned char c = '\0';
       switch (BT->getKind()) {
@@ -598,6 +575,46 @@
       Out << c;
       return;
     }
+
+    // If we have already seen this (non-built-in) type, use a substitution
+    // encoding.
+    llvm::DenseMap<const Type *, unsigned>::iterator Substitution
+      = TypeSubstitutions.find(T.getTypePtr());
+    if (Substitution != TypeSubstitutions.end()) {
+      Out << 'S' << Substitution->second << '_';
+      return;
+    } else {
+      // Record this as a substitution.
+      unsigned Number = TypeSubstitutions.size();
+      TypeSubstitutions[T.getTypePtr()] = Number;
+    }
+    
+    if (const PointerType *PT = T->getAs<PointerType>()) {
+      Out << '*';
+      T = PT->getPointeeType();
+      continue;
+    }
+    if (const ReferenceType *RT = T->getAs<ReferenceType>()) {
+      Out << '&';
+      T = RT->getPointeeType();
+      continue;
+    }
+    if (const FunctionProtoType *FT = T->getAs<FunctionProtoType>()) {
+      Out << 'F';
+      VisitType(FT->getResultType());
+      for (FunctionProtoType::arg_type_iterator
+            I = FT->arg_type_begin(), E = FT->arg_type_end(); I!=E; ++I) {
+        VisitType(*I);
+      }
+      if (FT->isVariadic())
+        Out << '.';
+      return;
+    }
+    if (const BlockPointerType *BT = T->getAs<BlockPointerType>()) {
+      Out << 'B';
+      T = BT->getPointeeType();
+      continue;
+    }
     if (const ComplexType *CT = T->getAs<ComplexType>()) {
       Out << '<';
       T = CT->getElementType();