diff --git a/lib/coffee-script/lexer.js b/lib/coffee-script/lexer.js
index 4c4f2850..37ab04ad 100644
--- a/lib/coffee-script/lexer.js
+++ b/lib/coffee-script/lexer.js
@@ -242,7 +242,9 @@
             if (i === $) {
               value = value.replace(TRAILING_BLANK_LINE, '');
             }
-            value = value.replace(indentRegex, '');
+            if (indentRegex) {
+              value = value.replace(indentRegex, '');
+            }
             return value;
           };
         })(this));
diff --git a/src/lexer.coffee b/src/lexer.coffee
index 7bf28be7..ea7e54a8 100644
--- a/src/lexer.coffee
+++ b/src/lexer.coffee
@@ -217,7 +217,7 @@ exports.Lexer = class Lexer
         value = @formatString value
         value = value.replace LEADING_BLANK_LINE,  '' if i is 0
         value = value.replace TRAILING_BLANK_LINE, '' if i is $
-        value = value.replace indentRegex, ''
+        value = value.replace indentRegex, '' if indentRegex
         value
     else
       @mergeInterpolationTokens tokens, {delimiter}, (value, i) =>
diff --git a/test/strings.coffee b/test/strings.coffee
index 7797b291..6eb314d5 100644
--- a/test/strings.coffee
+++ b/test/strings.coffee
@@ -342,6 +342,9 @@ eq """ "\\\" """, ' "\\" '
 
 eq '''  <- keep these spaces ->  ''', '  <- keep these spaces ->  '
 
+eq '''undefined''', 'undefined'
+eq """undefined""", 'undefined'
+
 
 test "#1046, empty string interpolations", ->
   eq "#{ }", ''