diff --git a/lib/less/parser.js b/lib/less/parser.js
index c32852d..5ddc217 100644
--- a/lib/less/parser.js
+++ b/lib/less/parser.js
@@ -311,9 +311,9 @@ less.Parser = function Parser(env) {
                             message: e.message,
                             filename: env.filename,
                             index: e.index,
-                            line: line + 1,
+                            line: typeof(line) === 'number' ? line + 1 : null,
                             callLine: e.call && (getLine(e.call) + 1),
-                            callExtract: lines[getLine(e.call) - 1],
+                            callExtract: lines[getLine(e.call)],
                             stack: e.stack,
                             column: column,
                             extract: [
@@ -330,7 +330,7 @@ less.Parser = function Parser(env) {
                     }
 
                     function getLine(index) {
-                        return (input.slice(0, index).match(/\n/g) || "").length;
+                        return index ? (input.slice(0, index).match(/\n/g) || "").length : null;
                     }
                 };
             })(root.toCSS);
diff --git a/lib/less/tree/mixin.js b/lib/less/tree/mixin.js
index c34a288..175f53f 100644
--- a/lib/less/tree/mixin.js
+++ b/lib/less/tree/mixin.js
@@ -19,7 +19,7 @@ tree.mixin.Call.prototype = {
                                   rules, mixins[m].eval(this.arguments, env).rules);
                             match = true;
                         } catch (e) {
-                            throw { message: e.message, index: e.index, call: this.index };
+                            throw { message: e.message, index: e.index, stack: e.stack, call: this.index };
                         }
                     }
                 }