diff --git a/src/compiler/parser.ts b/src/compiler/parser.ts
index 57e23531398..5ab0dad085f 100644
--- a/src/compiler/parser.ts
+++ b/src/compiler/parser.ts
@@ -1062,6 +1062,11 @@ module ts {
             if (node.kind === SyntaxKind.NumericLiteral && (isInStrictMode || languageVersion >= ScriptTarget.ES5)) {
                 var numberLiteralSource = getSourceTextOfNodeFromSourceText(sourceText, node);
                 // This regex checks if the number is written in octal
+                // Note that theoretically would match literals like 009, which is not octal. But because
+                // of how the scanner separates the tokens, we would never get a token like this. Instead,
+                // we would get 00 and 9 as two separate tokens.
+                // We also do not need to check for negatives because any prefix operator would be part of a
+                // parent unary expression.
                 if (/0[0-7]+/.test(numberLiteralSource)) {
                     if (isInStrictMode) {
                         grammarErrorOnNode(node, Diagnostics.Octal_literals_are_not_allowed_in_strict_mode);
diff --git a/tests/baselines/reference/scannerNumericLiteral8.errors.txt b/tests/baselines/reference/scannerNumericLiteral8.errors.txt
new file mode 100644
index 00000000000..a55568d91e0
--- /dev/null
+++ b/tests/baselines/reference/scannerNumericLiteral8.errors.txt
@@ -0,0 +1,4 @@
+==== tests/cases/conformance/scanner/ecmascript5/scannerNumericLiteral8.ts (1 errors) ====
+    -03
+     ~~
+!!! Octal literals are not available when targeting ECMAScript 5 and higher.
\ No newline at end of file
diff --git a/tests/baselines/reference/scannerNumericLiteral9.errors.txt b/tests/baselines/reference/scannerNumericLiteral9.errors.txt
new file mode 100644
index 00000000000..610c1c0a5fc
--- /dev/null
+++ b/tests/baselines/reference/scannerNumericLiteral9.errors.txt
@@ -0,0 +1,6 @@
+==== tests/cases/conformance/scanner/ecmascript5/scannerNumericLiteral9.ts (2 errors) ====
+    009
+    ~~
+!!! Octal literals are not available when targeting ECMAScript 5 and higher.
+      ~
+!!! ';' expected.
\ No newline at end of file
diff --git a/tests/cases/conformance/scanner/ecmascript5/scannerNumericLiteral8.ts b/tests/cases/conformance/scanner/ecmascript5/scannerNumericLiteral8.ts
new file mode 100644
index 00000000000..858e3eada0f
--- /dev/null
+++ b/tests/cases/conformance/scanner/ecmascript5/scannerNumericLiteral8.ts
@@ -0,0 +1,2 @@
+// @target: ES5
+-03
\ No newline at end of file
diff --git a/tests/cases/conformance/scanner/ecmascript5/scannerNumericLiteral9.ts b/tests/cases/conformance/scanner/ecmascript5/scannerNumericLiteral9.ts
new file mode 100644
index 00000000000..cf187b83edf
--- /dev/null
+++ b/tests/cases/conformance/scanner/ecmascript5/scannerNumericLiteral9.ts
@@ -0,0 +1,2 @@
+// @target: ES5
+009
\ No newline at end of file