diff --git a/compiler/java/com/google/dart/compiler/backend/js/GenerateNamesAndScopes.java b/compiler/java/com/google/dart/compiler/backend/js/GenerateNamesAndScopes.java
index 84fd758ba57..771f984ca04 100644
--- a/compiler/java/com/google/dart/compiler/backend/js/GenerateNamesAndScopes.java
+++ b/compiler/java/com/google/dart/compiler/backend/js/GenerateNamesAndScopes.java
@@ -49,7 +49,8 @@ class GenerateNamesAndScopes extends NormalizedVisitor {
 
   private final Deque<JsScope> scopes = new LinkedList<JsScope>();
   private DartClass currentClass = null;
-  private int nextLabelId = 0;
+  private int labelUniqifier = 0; // to resolve label name collisions.
+  private int varUniqifier = 0; // to resolve variable name collisions.
 
   private final TranslationContext translationContext;
   private final LibraryElement unitLibrary;
@@ -124,20 +125,20 @@ class GenerateNamesAndScopes extends NormalizedVisitor {
   public boolean visit(DartParameter x, DartContext ctx) {
     // TODO(ngeoffray): A parameter in a function type does not have a symbol.
     if (x.getSymbol() != null) {
-      declare(x.getSymbol(), x.getParameterName());
+      declareExclusively(x.getSymbol(), x.getParameterName());
     }
     return true;
   }
 
   @Override
   public boolean visit(DartVariable x, DartContext ctx) {
-    declare(x.getSymbol(), x.getVariableName());
+    declareExclusively(x.getSymbol(), x.getVariableName());
     return true;
   }
 
   @Override
   public boolean visit(DartLabel x, DartContext ctx) {
-    declare(x.getSymbol(), "L" + nextLabelId++);
+    declareExclusively(x.getSymbol(), String.format("L%X", labelUniqifier++));
     return true;
   }
 
@@ -163,7 +164,7 @@ class GenerateNamesAndScopes extends NormalizedVisitor {
   }
 
   private JsName function(Symbol symbol, String name, String originalName, DartFunction func) {
-    JsName jsName = name != null ? declare(symbol, name, originalName) : null;
+    JsName jsName = name != null ? declareExclusively(symbol, name, originalName) : null;
     JsFunction jsFunc = new JsFunction(scopes.peek(), jsName);
     jsFunc.setFromDart(true);
     scopes.push(jsFunc.getScope());
@@ -175,8 +176,32 @@ class GenerateNamesAndScopes extends NormalizedVisitor {
     return declareInScope(scopes.peek(), x, name, originalName);
   }
 
-  private JsName declare(Symbol x, String name) {
-    return declareInScope(scopes.peek(), x, name, name);
+  private JsName declareExclusively(Symbol x, String name, String originalName) {
+    return declareExclusivelyInScope(scopes.peek(), x, name, originalName);
+  }
+
+  private JsName declareExclusively(Symbol x, String name) {
+    return declareExclusivelyInScope(scopes.peek(), x, name, name);
+  }
+
+  private static final int BIG_PRIME_UNDER_0XFFFFF = 985531;
+
+  /**
+   * Create a unique name for this variable in this scope.
+   *
+   * Try to keep this from being a linear scan of the namespace, and keep
+   * it under 5 hex digits (over 1,000,000 unique suffixes).
+   *
+   */
+  private JsName declareExclusivelyInScope(JsScope scope, Symbol x,
+                                           String name, String originalName) {
+    String mappedName = name;
+    int offset = 0;
+    while (scope.findExistingName(mappedName) != null) {
+      mappedName = String.format("%s_%X", mappedName, varUniqifier);
+      varUniqifier = (varUniqifier + offset++) % BIG_PRIME_UNDER_0XFFFFF;
+    }
+    return declareInScope(scope, x, mappedName, originalName);
   }
 
   private JsName declareInScope(JsScope scope, Symbol x, String name, String originalName) {
diff --git a/tests/co19/co19-compiler.status b/tests/co19/co19-compiler.status
index 2f011641b5b..04ec4d44541 100644
--- a/tests/co19/co19-compiler.status
+++ b/tests/co19/co19-compiler.status
@@ -137,9 +137,7 @@ LangGuideTest/02_Language_Constructs/02_1_Class/02_1_Class_Construction/A13/t01:
 LangGuideTest/02_Language_Constructs/02_1_Class/02_1_Class_Construction/A18/t01: Fail # Bug 5371670.
 LangGuideTest/02_Language_Constructs/02_2_Interface/A02/t03: Fail # Bug 5371670.
 LangGuideTest/02_Language_Constructs/02_5_Meaning_of_Names/Examples/A02/t01: Fail # Bug 5371670.
-LangGuideTest/02_Language_Constructs/02_5_Meaning_of_Names/Shadowing_and_Hiding_Names/A01/t01: Fail # Bug 5371670.
-LangGuideTest/02_Language_Constructs/02_5_Meaning_of_Names/Shadowing_and_Hiding_Names/A02/t01: Fail # Bug 5371670.
-LangGuideTest/02_Language_Constructs/02_5_Meaning_of_Names/Shadowing_and_Hiding_Names/A01/t02: Fail # Bug 5371670.
+
 LangGuideTest/02_Language_Constructs/02_7_Abstract_Methods/A02/t01: Fail # Bug 5371670.
 LangGuideTest/02_Language_Constructs/02_8_Static_Methods/A02/t02: Fail # Bug 5371670.
 LangGuideTest/07_Overriding/A02/t01: Fail # Bug 5371670.
@@ -253,7 +251,9 @@ LangGuideTest/02_Language_Constructs/02_11_Exceptions/A05/t01: Fail
 LangGuideTest/02_Language_Constructs/02_1_Class/02_1_Class_Construction/A05/t01: Fail
 LangGuideTest/02_Language_Constructs/02_1_Class/02_1_Class_Construction/A12/t02: Fail
 LangGuideTest/02_Language_Constructs/02_1_Class/A02/t04: Skip # Times out.
-LangGuideTest/02_Language_Constructs/02_5_Meaning_of_Names/A02/t02: Fail
+LangGuideTest/02_Language_Constructs/02_5_Meaning_of_Names/Shadowing_and_Hiding_Names/A01/t01: Fail
+LangGuideTest/02_Language_Constructs/02_5_Meaning_of_Names/Shadowing_and_Hiding_Names/A02/t01: Fail
+LangGuideTest/02_Language_Constructs/02_5_Meaning_of_Names/Shadowing_and_Hiding_Names/A01/t02: Fail
 LangGuideTest/02_Language_Constructs/02_6_Functions/A04/t01: Fail
 LangGuideTest/02_Language_Constructs/02_6_Functions/A06/t01: Fail
 LangGuideTest/02_Language_Constructs/02_6_Functions/A06/t02: Fail
diff --git a/tests/language/language.status b/tests/language/language.status
index f887d584cd5..87625558b30 100644
--- a/tests/language/language.status
+++ b/tests/language/language.status
@@ -67,7 +67,6 @@ BadNamedParametersTest: Fail    # Bug Bug 4202974 - release mode is not throwing
 Prefix11NegativeTest: Fail # Bug 5406175
 Prefix12NegativeTest: Fail # Bug 5406175
 FunctionTypeParameterNegativeTest: Fail # Bug 4568007
-ImplicitScopeTest: FAIL              # Nested statements can be declarations
 ConstConstructor1NegativeTest: FAIL  # 5142545
 ConstConstructor2NegativeTest: FAIL  # 5142545
 MathTest: FAIL                       # 5165080
@@ -80,7 +79,6 @@ NamedParameters2NegativeTest: Fail   # Implementation in progress.
 NamedParameters3NegativeTest: Fail   # Implementation in progress.
 NamedParameters4NegativeTest: Fail   # Implementation in progress.
 NamedParameters6NegativeTest: Crash  # Implementation in progress.
-ScopeVariableTest: Fail              # 5244704
 InstFieldInitializerTest: Fail       # Cannot deal with static final values in const expression.
 RegExp3Test: Fail                    # 5299683
 InterfaceFactory3NegativeTest: Fail  # 5387405