diff --git a/AST.cpp b/AST.cpp
index cef3c4b..ed58a37 100644
--- a/AST.cpp
+++ b/AST.cpp
@@ -38,7 +38,7 @@
 AST::AST(const Coordinator* coordinator, const std::string& path)
     : mCoordinator(coordinator),
       mPath(path),
-      mRootScope("(root scope)", Location::startOf(path), nullptr /* parent */) {}
+      mRootScope("(root scope)", FQName(), Location::startOf(path), nullptr /* parent */) {}
 
 Scope* AST::getRootScope() {
     return &mRootScope;
@@ -84,6 +84,11 @@
 
 status_t AST::postParse() {
     status_t err;
+    // validateDefinedTypesUniqueNames is the first call,
+    // as other errors could appear because user meant
+    // different type than we assumed.
+    err = validateDefinedTypesUniqueNames();
+    if (err != OK) return err;
     // checkAcyclicTypes is before resolveInheritance, as we
     // need to have no cycle while getting parent class.
     err = checkAcyclicTypes();
@@ -133,6 +138,19 @@
         &visitedTypes);
 }
 
+status_t AST::validateDefinedTypesUniqueNames() const {
+    std::unordered_set<const Type*> visited;
+    return mRootScope.recursivePass(
+        [&](const Type* type) -> status_t {
+            // We only want to validate type definition names in this place.
+            if (type->isScope()) {
+                return static_cast<const Scope*>(type)->validateUniqueNames();
+            }
+            return OK;
+        },
+        &visited);
+}
+
 status_t AST::resolveInheritance() {
     std::unordered_set<const Type*> visited;
     return mRootScope.recursivePass(&Type::resolveInheritance, &visited);
@@ -278,13 +296,8 @@
     mImportedASTs.insert(ast);
 }
 
-bool AST::addScopedType(NamedType* type, std::string* errorMsg, Scope* scope) {
-    bool success = scope->addType(type, errorMsg);
-    if (!success) {
-        return false;
-    }
-
-    std::vector<std::string> pathComponents{{type->localName()}};
+FQName AST::makeFullName(const char* localName, Scope* scope) const {
+    std::vector<std::string> pathComponents{{localName}};
     for (; scope != &mRootScope; scope = scope->parent()) {
         pathComponents.push_back(scope->localName());
     }
@@ -292,12 +305,12 @@
     std::reverse(pathComponents.begin(), pathComponents.end());
     std::string path = StringHelper::JoinStrings(pathComponents, ".");
 
-    FQName fqName(mPackage.package(), mPackage.version(), path);
-    type->setFullName(fqName);
+    return FQName(mPackage.package(), mPackage.version(), path);
+}
 
-    mDefinedTypesByFullName[fqName] = type;
-
-    return true;
+void AST::addScopedType(NamedType* type, Scope* scope) {
+    scope->addType(type);
+    mDefinedTypesByFullName[type->fqName()] = type;
 }
 
 EnumValue* AST::lookupEnumValue(const FQName& fqName, std::string* errorMsg, Scope* scope) {
diff --git a/AST.h b/AST.h
index f77c0b7..0f27c85 100644
--- a/AST.h
+++ b/AST.h
@@ -54,8 +54,10 @@
     bool isInterface() const;
     bool containsInterfaces() const;
 
-    // Returns true iff successful.
-    bool addScopedType(NamedType* type, std::string* errorMsg, Scope* scope);
+    // Adds package, version and scope stack to local name
+    FQName makeFullName(const char* localName, Scope* scope) const;
+
+    void addScopedType(NamedType* type, Scope* scope);
 
     const std::string &getFilename() const;
 
@@ -77,6 +79,10 @@
     status_t constantExpressionRecursivePass(
         const std::function<status_t(ConstantExpression*)>& func);
 
+    // Recursive tree pass that validates that all defined types
+    // have unique names in their scopes.
+    status_t validateDefinedTypesUniqueNames() const;
+
     // Recursive tree pass that completes type declarations
     // that depend on super types
     status_t resolveInheritance();
diff --git a/CompoundType.cpp b/CompoundType.cpp
index 4211958..0254a6c 100644
--- a/CompoundType.cpp
+++ b/CompoundType.cpp
@@ -26,9 +26,9 @@
 
 namespace android {
 
-CompoundType::CompoundType(Style style, const char* localName, const Location& location,
-                           Scope* parent)
-    : Scope(localName, location, parent), mStyle(style), mFields(NULL) {}
+CompoundType::CompoundType(Style style, const char* localName, const FQName& fullName,
+                           const Location& location, Scope* parent)
+    : Scope(localName, fullName, location, parent), mStyle(style), mFields(NULL) {}
 
 CompoundType::Style CompoundType::style() const {
     return mStyle;
diff --git a/CompoundType.h b/CompoundType.h
index a5dd7fc..0e61c28 100644
--- a/CompoundType.h
+++ b/CompoundType.h
@@ -31,7 +31,8 @@
         STYLE_UNION,
     };
 
-    CompoundType(Style style, const char* localName, const Location& location, Scope* parent);
+    CompoundType(Style style, const char* localName, const FQName& fullName,
+                 const Location& location, Scope* parent);
 
     Style style() const;
 
diff --git a/EnumType.cpp b/EnumType.cpp
index edfbf47..1ed3849 100644
--- a/EnumType.cpp
+++ b/EnumType.cpp
@@ -27,9 +27,9 @@
 
 namespace android {
 
-EnumType::EnumType(const char* localName, const Location& location,
+EnumType::EnumType(const char* localName, const FQName& fullName, const Location& location,
                    const Reference<Type>& storageType, Scope* parent)
-    : Scope(localName, location, parent),
+    : Scope(localName, fullName, location, parent),
       mValues(),
       mStorageType(storageType),
       mBitfieldType(new BitFieldType(parent)) {
diff --git a/EnumType.h b/EnumType.h
index c5cd662..51dd454 100644
--- a/EnumType.h
+++ b/EnumType.h
@@ -30,8 +30,8 @@
 struct BitFieldType;
 
 struct EnumType : public Scope {
-    EnumType(const char* localName, const Location& location, const Reference<Type>& storageType,
-             Scope* parent);
+    EnumType(const char* localName, const FQName& fullName, const Location& location,
+             const Reference<Type>& storageType, Scope* parent);
 
     const Type *storageType() const;
     const std::vector<EnumValue *> &values() const;
diff --git a/Interface.cpp b/Interface.cpp
index 1ae6638..0fcd081 100644
--- a/Interface.cpp
+++ b/Interface.cpp
@@ -69,9 +69,9 @@
     LAST_HIDL_TRANSACTION   = 0x0fffffff,
 };
 
-Interface::Interface(const char* localName, const Location& location, Scope* parent,
-                     const Reference<Type>& superType)
-    : Scope(localName, location, parent),
+Interface::Interface(const char* localName, const FQName& fullName, const Location& location,
+                     Scope* parent, const Reference<Type>& superType)
+    : Scope(localName, fullName, location, parent),
       mSuperType(superType),
       mIsJavaCompatibleInProgress(false) {}
 
diff --git a/Interface.h b/Interface.h
index 02b0f4d..0a15bf9 100644
--- a/Interface.h
+++ b/Interface.h
@@ -29,8 +29,8 @@
 struct InterfaceAndMethod;
 
 struct Interface : public Scope {
-    Interface(const char* localName, const Location& location, Scope* parent,
-              const Reference<Type>& superType);
+    Interface(const char* localName, const FQName& fullName, const Location& location,
+              Scope* parent, const Reference<Type>& superType);
 
     bool addMethod(Method *method);
     bool addAllReservedMethods();
diff --git a/NamedType.cpp b/NamedType.cpp
index c0c8450..a57c8cd 100644
--- a/NamedType.cpp
+++ b/NamedType.cpp
@@ -18,17 +18,14 @@
 
 namespace android {
 
-NamedType::NamedType(const char* localName, const Location& loc, Scope* parent)
-    : Type(parent), mLocalName(localName), mLocation(loc) {}
+NamedType::NamedType(const char* localName, const FQName& fullName, const Location& loc,
+                     Scope* parent)
+    : Type(parent), mLocalName(localName), mFullName(fullName), mLocation(loc) {}
 
 bool NamedType::isNamedType() const {
     return true;
 }
 
-void NamedType::setFullName(const FQName &fullName) {
-    mFullName = fullName;
-}
-
 const FQName &NamedType::fqName() const {
     return mFullName;
 }
diff --git a/NamedType.h b/NamedType.h
index f666ba1..a0ef302 100644
--- a/NamedType.h
+++ b/NamedType.h
@@ -28,12 +28,10 @@
 namespace android {
 
 struct NamedType : public Type {
-    NamedType(const char* localName, const Location& loc, Scope* parent);
+    NamedType(const char* localName, const FQName& fullName, const Location& loc, Scope* parent);
 
     bool isNamedType() const override;
 
-    void setFullName(const FQName &fullName);
-
     const FQName &fqName() const;
 
     std::string localName() const;
@@ -54,7 +52,7 @@
 
    private:
     const std::string mLocalName;
-    FQName mFullName;
+    const FQName mFullName;
     const Location mLocation;
 
     DISALLOW_COPY_AND_ASSIGN(NamedType);
diff --git a/Scope.cpp b/Scope.cpp
index 64ccd2e..b9f90b9 100644
--- a/Scope.cpp
+++ b/Scope.cpp
@@ -22,32 +22,30 @@
 
 #include <android-base/logging.h>
 #include <hidl-util/Formatter.h>
+#include <iostream>
 #include <vector>
 
 namespace android {
 
-Scope::Scope(const char* localName, const Location& location, Scope* parent)
-    : NamedType(localName, location, parent) {}
+Scope::Scope(const char* localName, const FQName& fullName, const Location& location, Scope* parent)
+    : NamedType(localName, fullName, location, parent) {}
 Scope::~Scope(){}
 
-bool Scope::addType(NamedType *type, std::string *errorMsg) {
-    const std::string &localName = type->localName();
-
-    auto it = mTypeIndexByName.find(localName);
-
-    if (it != mTypeIndexByName.end()) {
-        *errorMsg = "A type named '";
-        (*errorMsg) += localName;
-        (*errorMsg) += "' is already declared in the  current scope.";
-
-        return false;
-    }
-
+void Scope::addType(NamedType* type) {
     size_t index = mTypes.size();
     mTypes.push_back(type);
-    mTypeIndexByName[localName] = index;
+    mTypeIndexByName[type->localName()] = index;
+}
 
-    return true;
+status_t Scope::validateUniqueNames() const {
+    for (const auto* type : mTypes) {
+        if (mTypes[mTypeIndexByName.at(type->localName())] != type) {
+            std::cerr << "ERROR: A type named '" << type->localName()
+                      << "' is already declared in the scope at " << type->location() << "\n";
+            return UNKNOWN_ERROR;
+        }
+    }
+    return OK;
 }
 
 NamedType *Scope::lookupType(const FQName &fqName) const {
@@ -218,8 +216,9 @@
 
 ////////////////////////////////////////
 
-RootScope::RootScope(const char* localName, const Location& location, Scope* parent)
-    : Scope(localName, location, parent) {}
+RootScope::RootScope(const char* localName, const FQName& fullName, const Location& location,
+                     Scope* parent)
+    : Scope(localName, fullName, location, parent) {}
 RootScope::~RootScope() {}
 
 std::string RootScope::typeName() const {
diff --git a/Scope.h b/Scope.h
index 848352c..25ffb7e 100644
--- a/Scope.h
+++ b/Scope.h
@@ -32,10 +32,12 @@
 struct LocalIdentifier;
 
 struct Scope : public NamedType {
-    Scope(const char* localName, const Location& location, Scope* parent);
+    Scope(const char* localName, const FQName& fullName, const Location& location, Scope* parent);
     virtual ~Scope();
 
-    bool addType(NamedType *type, std::string *errorMsg);
+    void addType(NamedType* type);
+
+    status_t validateUniqueNames() const;
 
     // lookup a type given an FQName.
     // Assume fqName.package(), fqName.version(), fqName.valueName() is empty.
@@ -88,7 +90,8 @@
 };
 
 struct RootScope : public Scope {
-    RootScope(const char* localName, const Location& location, Scope* parent);
+    RootScope(const char* localName, const FQName& fullName, const Location& location,
+              Scope* parent);
     virtual ~RootScope();
 
     virtual status_t validate() const override;
diff --git a/TypeDef.cpp b/TypeDef.cpp
index 6295746..1592778 100644
--- a/TypeDef.cpp
+++ b/TypeDef.cpp
@@ -21,9 +21,9 @@
 
 namespace android {
 
-TypeDef::TypeDef(const char* localName, const Location& location, Scope* parent,
-                 const Reference<Type>& type)
-    : NamedType(localName, location, parent), mReferencedType(type) {}
+TypeDef::TypeDef(const char* localName, const FQName& fullName, const Location& location,
+                 Scope* parent, const Reference<Type>& type)
+    : NamedType(localName, fullName, location, parent), mReferencedType(type) {}
 
 const ScalarType *TypeDef::resolveToScalarType() const {
     CHECK(!"Should not be here");
diff --git a/TypeDef.h b/TypeDef.h
index 19af261..0e380fa 100644
--- a/TypeDef.h
+++ b/TypeDef.h
@@ -23,7 +23,7 @@
 namespace android {
 
 struct TypeDef : public NamedType {
-    TypeDef(const char* localName, const Location& location, Scope* parent,
+    TypeDef(const char* localName, const FQName& fullName, const Location& location, Scope* parent,
             const Reference<Type>& type);
 
     const ScalarType *resolveToScalarType() const override;
diff --git a/hidl-gen_y.yy b/hidl-gen_y.yy
index a3ceb53..f1a19aa 100644
--- a/hidl-gen_y.yy
+++ b/hidl-gen_y.yy
@@ -675,15 +675,11 @@
           }
 
           Interface* iface = new Interface(
-              $2, convertYYLoc(@2), *scope, *superType);
+              $2, ast->makeFullName($2, *scope), convertYYLoc(@2), *scope, *superType);
 
           // Register interface immediately so it can be referenced inside
           // definition.
-          std::string errorMsg;
-          if (!ast->addScopedType(iface, &errorMsg, *scope)) {
-              std::cerr << "ERROR: " << errorMsg << " at " << @2 << "\n";
-              YYERROR;
-          }
+          ast->addScopedType(iface, *scope);
 
           enterScope(ast, scope, iface);
       }
@@ -706,14 +702,9 @@
           // The reason we wrap the given type in a TypeDef is simply to suppress
           // emitting any type definitions later on, since this is just an alias
           // to a type defined elsewhere.
-          TypeDef* typeDef = new TypeDef($3, convertYYLoc(@2), *scope, *$2);
-
-          std::string errorMsg;
-          if (!ast->addScopedType(typeDef, &errorMsg, *scope)) {
-              std::cerr << "ERROR: " << errorMsg << " at " << @3 << "\n";
-              YYERROR;
-          }
-
+          TypeDef* typeDef = new TypeDef(
+              $3, ast->makeFullName($3, *scope), convertYYLoc(@2), *scope, *$2);
+          ast->addScopedType(typeDef, *scope);
           $$ = typeDef;
       }
     ;
@@ -854,7 +845,8 @@
 named_struct_or_union_declaration
     : struct_or_union_keyword valid_type_name
       {
-          CompoundType *container = new CompoundType($1, $2, convertYYLoc(@2), *scope);
+          CompoundType *container = new CompoundType(
+              $1, $2, ast->makeFullName($2, *scope), convertYYLoc(@2), *scope);
           enterScope(ast, scope, container);
       }
       struct_or_union_body
@@ -864,13 +856,7 @@
           container->setFields($4);
 
           leaveScope(ast, scope);
-
-          std::string errorMsg;
-          if (!ast->addScopedType(container, &errorMsg, *scope)) {
-              std::cerr << "ERROR: " << errorMsg << " at " << @2 << "\n";
-              YYERROR;
-          }
-
+          ast->addScopedType(container, *scope);
           $$ = container;
       }
     ;
@@ -950,21 +936,17 @@
 named_enum_declaration
     : ENUM valid_type_name enum_storage_type
       {
-          enterScope(ast, scope, new EnumType($2, convertYYLoc(@2), *$3, *scope));
+          EnumType* enumType = new EnumType(
+              $2, ast->makeFullName($2, *scope), convertYYLoc(@2), *$3, *scope);
+          enterScope(ast, scope, enumType);
       }
       enum_declaration_body
       {
           CHECK((*scope)->isEnum());
+          EnumType* enumType = static_cast<EnumType*>(*scope);
 
-          EnumType *enumType = static_cast<EnumType *>(*scope);
           leaveScope(ast, scope);
-
-          std::string errorMsg;
-          if (!ast->addScopedType(enumType, &errorMsg, *scope)) {
-              std::cerr << "ERROR: " << errorMsg << " at " << @2 << "\n";
-              YYERROR;
-          }
-
+          ast->addScopedType(enumType, *scope);
           $$ = enumType;
       }
     ;
diff --git a/test/error_test/Android.bp b/test/error_test/Android.bp
index b7481ce..260f34c 100644
--- a/test/error_test/Android.bp
+++ b/test/error_test/Android.bp
@@ -45,6 +45,9 @@
          "!($(location hidl-gen) -L check -r test:system/tools/hidl/test/error_test" +
          "    test.interface_unique_method_names_inheritance@1.0  >/dev/null 2>&1)" +
          "&&" +
+         "!($(location hidl-gen) -L check -r test:system/tools/hidl/test/error_test" +
+         "    test.scope_unique_type_names@1.0  >/dev/null 2>&1)" +
+         "&&" +
          "echo 'int main(){return 0;}' > $(genDir)/TODO_b_37575883.cpp",
     out: ["TODO_b_37575883.cpp"],
     srcs: [
@@ -60,6 +63,7 @@
         "no_two_interfaces/1.0/IFoo.hal",
         "same_name_interface/1.0/IFoo.hal",
         "same_package_name/1.0/IFoo.hal",
+        "scope_unique_type_names/1.0/IFoo.hal",
     ],
 }
 
diff --git a/test/error_test/scope_unique_type_names/1.0/IFoo.hal b/test/error_test/scope_unique_type_names/1.0/IFoo.hal
new file mode 100644
index 0000000..815c8a2
--- /dev/null
+++ b/test/error_test/scope_unique_type_names/1.0/IFoo.hal
@@ -0,0 +1,21 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package test.scope_unique_type_names@1.0;
+
+interface IFoo {
+    struct S {};
+    enum S : int32_t {};  // duplicates first struct name
+};