diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 04766f22c4e..e81da871809 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -7897,7 +7897,7 @@ module ts {
         function checkYieldExpression(node: YieldExpression): void {
             // Grammar checking
             if (!(node.parserContextFlags & ParserContextFlags.Yield)) {
-                grammarErrorOnFirstToken(node, Diagnostics.yield_expression_must_be_contained_within_a_generator_declaration);
+                grammarErrorOnFirstToken(node, Diagnostics.A_yield_expression_is_only_allowed_in_a_generator_declaration);
             }
             else {
                 grammarErrorOnFirstToken(node, Diagnostics.yield_expressions_are_not_currently_supported);
diff --git a/src/compiler/diagnosticInformationMap.generated.ts b/src/compiler/diagnosticInformationMap.generated.ts
index 14163e81195..21c953e21c2 100644
--- a/src/compiler/diagnosticInformationMap.generated.ts
+++ b/src/compiler/diagnosticInformationMap.generated.ts
@@ -120,7 +120,7 @@ module ts {
         Unterminated_template_literal: { code: 1160, category: DiagnosticCategory.Error, key: "Unterminated template literal." },
         Unterminated_regular_expression_literal: { code: 1161, category: DiagnosticCategory.Error, key: "Unterminated regular expression literal." },
         An_object_member_cannot_be_declared_optional: { code: 1162, category: DiagnosticCategory.Error, key: "An object member cannot be declared optional." },
-        yield_expression_must_be_contained_within_a_generator_declaration: { code: 1163, category: DiagnosticCategory.Error, key: "'yield' expression must be contained_within a generator declaration." },
+        A_yield_expression_is_only_allowed_in_a_generator_declaration: { code: 1163, category: DiagnosticCategory.Error, key: "A 'yield' expression is only allowed in a generator declaration." },
         Computed_property_names_are_not_allowed_in_enums: { code: 1164, category: DiagnosticCategory.Error, key: "Computed property names are not allowed in enums." },
         A_computed_property_name_in_an_ambient_context_must_directly_refer_to_a_built_in_symbol: { code: 1165, category: DiagnosticCategory.Error, key: "A computed property name in an ambient context must directly refer to a built-in symbol." },
         A_computed_property_name_in_a_class_property_declaration_must_directly_refer_to_a_built_in_symbol: { code: 1166, category: DiagnosticCategory.Error, key: "A computed property name in a class property declaration must directly refer to a built-in symbol." },
diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
index 18c98928dda..f7ca2171fea 100644
--- a/src/compiler/diagnosticMessages.json
+++ b/src/compiler/diagnosticMessages.json
@@ -467,7 +467,7 @@
         "category": "Error",
         "code": 1162
     },
-    "'yield' expression must be contained_within a generator declaration.": {
+    "A 'yield' expression is only allowed in a generator declaration.": {
         "category": "Error",
         "code": 1163
     },
diff --git a/tests/baselines/reference/YieldExpression12_es6.errors.txt b/tests/baselines/reference/YieldExpression12_es6.errors.txt
index 10843421a3f..3f007c07b6d 100644
--- a/tests/baselines/reference/YieldExpression12_es6.errors.txt
+++ b/tests/baselines/reference/YieldExpression12_es6.errors.txt
@@ -1,4 +1,4 @@
-tests/cases/conformance/es6/yieldExpressions/YieldExpression12_es6.ts(3,6): error TS1163: 'yield' expression must be contained_within a generator declaration.
+tests/cases/conformance/es6/yieldExpressions/YieldExpression12_es6.ts(3,6): error TS1163: A 'yield' expression is only allowed in a generator declaration.
 
 
 ==== tests/cases/conformance/es6/yieldExpressions/YieldExpression12_es6.ts (1 errors) ====
@@ -6,6 +6,6 @@ tests/cases/conformance/es6/yieldExpressions/YieldExpression12_es6.ts(3,6): erro
       constructor() {
          yield foo
          ~~~~~
-!!! error TS1163: 'yield' expression must be contained_within a generator declaration.
+!!! error TS1163: A 'yield' expression is only allowed in a generator declaration.
       }
     }
\ No newline at end of file
diff --git a/tests/baselines/reference/YieldExpression14_es6.errors.txt b/tests/baselines/reference/YieldExpression14_es6.errors.txt
index baeaf3ba30e..3a47ad2bf39 100644
--- a/tests/baselines/reference/YieldExpression14_es6.errors.txt
+++ b/tests/baselines/reference/YieldExpression14_es6.errors.txt
@@ -1,4 +1,4 @@
-tests/cases/conformance/es6/yieldExpressions/YieldExpression14_es6.ts(3,6): error TS1163: 'yield' expression must be contained_within a generator declaration.
+tests/cases/conformance/es6/yieldExpressions/YieldExpression14_es6.ts(3,6): error TS1163: A 'yield' expression is only allowed in a generator declaration.
 
 
 ==== tests/cases/conformance/es6/yieldExpressions/YieldExpression14_es6.ts (1 errors) ====
@@ -6,6 +6,6 @@ tests/cases/conformance/es6/yieldExpressions/YieldExpression14_es6.ts(3,6): erro
       foo() {
          yield foo
          ~~~~~
-!!! error TS1163: 'yield' expression must be contained_within a generator declaration.
+!!! error TS1163: A 'yield' expression is only allowed in a generator declaration.
       }
     }
\ No newline at end of file
diff --git a/tests/baselines/reference/YieldExpression15_es6.errors.txt b/tests/baselines/reference/YieldExpression15_es6.errors.txt
index 5e548799f5d..ded6fa9aeb8 100644
--- a/tests/baselines/reference/YieldExpression15_es6.errors.txt
+++ b/tests/baselines/reference/YieldExpression15_es6.errors.txt
@@ -1,9 +1,9 @@
-tests/cases/conformance/es6/yieldExpressions/YieldExpression15_es6.ts(2,6): error TS1163: 'yield' expression must be contained_within a generator declaration.
+tests/cases/conformance/es6/yieldExpressions/YieldExpression15_es6.ts(2,6): error TS1163: A 'yield' expression is only allowed in a generator declaration.
 
 
 ==== tests/cases/conformance/es6/yieldExpressions/YieldExpression15_es6.ts (1 errors) ====
     var v = () => {
          yield foo
          ~~~~~
-!!! error TS1163: 'yield' expression must be contained_within a generator declaration.
+!!! error TS1163: A 'yield' expression is only allowed in a generator declaration.
       }
\ No newline at end of file
diff --git a/tests/baselines/reference/YieldExpression16_es6.errors.txt b/tests/baselines/reference/YieldExpression16_es6.errors.txt
index c0d2e4c8fc8..304d4eca05c 100644
--- a/tests/baselines/reference/YieldExpression16_es6.errors.txt
+++ b/tests/baselines/reference/YieldExpression16_es6.errors.txt
@@ -1,5 +1,5 @@
 tests/cases/conformance/es6/yieldExpressions/YieldExpression16_es6.ts(1,9): error TS9001: Generators are not currently supported.
-tests/cases/conformance/es6/yieldExpressions/YieldExpression16_es6.ts(3,5): error TS1163: 'yield' expression must be contained_within a generator declaration.
+tests/cases/conformance/es6/yieldExpressions/YieldExpression16_es6.ts(3,5): error TS1163: A 'yield' expression is only allowed in a generator declaration.
 
 
 ==== tests/cases/conformance/es6/yieldExpressions/YieldExpression16_es6.ts (2 errors) ====
@@ -9,6 +9,6 @@ tests/cases/conformance/es6/yieldExpressions/YieldExpression16_es6.ts(3,5): erro
       function bar() {
         yield foo;
         ~~~~~
-!!! error TS1163: 'yield' expression must be contained_within a generator declaration.
+!!! error TS1163: A 'yield' expression is only allowed in a generator declaration.
       }
     }
\ No newline at end of file
diff --git a/tests/baselines/reference/YieldExpression17_es6.errors.txt b/tests/baselines/reference/YieldExpression17_es6.errors.txt
index b39f47b07f9..59b728ac495 100644
--- a/tests/baselines/reference/YieldExpression17_es6.errors.txt
+++ b/tests/baselines/reference/YieldExpression17_es6.errors.txt
@@ -1,6 +1,6 @@
 tests/cases/conformance/es6/yieldExpressions/YieldExpression17_es6.ts(1,15): error TS1056: Accessors are only available when targeting ECMAScript 5 and higher.
 tests/cases/conformance/es6/yieldExpressions/YieldExpression17_es6.ts(1,15): error TS2378: A 'get' accessor must return a value or consist of a single 'throw' statement.
-tests/cases/conformance/es6/yieldExpressions/YieldExpression17_es6.ts(1,23): error TS1163: 'yield' expression must be contained_within a generator declaration.
+tests/cases/conformance/es6/yieldExpressions/YieldExpression17_es6.ts(1,23): error TS1163: A 'yield' expression is only allowed in a generator declaration.
 
 
 ==== tests/cases/conformance/es6/yieldExpressions/YieldExpression17_es6.ts (3 errors) ====
@@ -10,4 +10,4 @@ tests/cases/conformance/es6/yieldExpressions/YieldExpression17_es6.ts(1,23): err
                   ~~~
 !!! error TS2378: A 'get' accessor must return a value or consist of a single 'throw' statement.
                           ~~~~~
-!!! error TS1163: 'yield' expression must be contained_within a generator declaration.
\ No newline at end of file
+!!! error TS1163: A 'yield' expression is only allowed in a generator declaration.
\ No newline at end of file
diff --git a/tests/baselines/reference/YieldExpression18_es6.errors.txt b/tests/baselines/reference/YieldExpression18_es6.errors.txt
index 3a67acdebcd..274592904ed 100644
--- a/tests/baselines/reference/YieldExpression18_es6.errors.txt
+++ b/tests/baselines/reference/YieldExpression18_es6.errors.txt
@@ -1,8 +1,8 @@
-tests/cases/conformance/es6/yieldExpressions/YieldExpression18_es6.ts(2,1): error TS1163: 'yield' expression must be contained_within a generator declaration.
+tests/cases/conformance/es6/yieldExpressions/YieldExpression18_es6.ts(2,1): error TS1163: A 'yield' expression is only allowed in a generator declaration.
 
 
 ==== tests/cases/conformance/es6/yieldExpressions/YieldExpression18_es6.ts (1 errors) ====
     "use strict";
     yield(foo);
     ~~~~~
-!!! error TS1163: 'yield' expression must be contained_within a generator declaration.
\ No newline at end of file
+!!! error TS1163: A 'yield' expression is only allowed in a generator declaration.
\ No newline at end of file
diff --git a/tests/baselines/reference/YieldExpression2_es6.errors.txt b/tests/baselines/reference/YieldExpression2_es6.errors.txt
index 553dab51fc2..280f0b88f93 100644
--- a/tests/baselines/reference/YieldExpression2_es6.errors.txt
+++ b/tests/baselines/reference/YieldExpression2_es6.errors.txt
@@ -1,7 +1,7 @@
-tests/cases/conformance/es6/yieldExpressions/YieldExpression2_es6.ts(1,1): error TS1163: 'yield' expression must be contained_within a generator declaration.
+tests/cases/conformance/es6/yieldExpressions/YieldExpression2_es6.ts(1,1): error TS1163: A 'yield' expression is only allowed in a generator declaration.
 
 
 ==== tests/cases/conformance/es6/yieldExpressions/YieldExpression2_es6.ts (1 errors) ====
     yield foo;
     ~~~~~
-!!! error TS1163: 'yield' expression must be contained_within a generator declaration.
\ No newline at end of file
+!!! error TS1163: A 'yield' expression is only allowed in a generator declaration.
\ No newline at end of file