diff --git a/package.json b/package.json
index 0e6f3fd..f57edb5 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "findandreplacedomtext",
-  "version": "0.4.5",
+  "version": "0.4.6",
   "main": "./src/findAndReplaceDOMText.js",
   "description": "findAndReplaceDOMText: DOM find/replace utility",
   "repository": {
diff --git a/readme.md b/readme.md
index 445fbf5..1c82391 100644
--- a/readme.md
+++ b/readme.md
@@ -262,6 +262,7 @@ exposed.PRESETS = {
 
 ### Changelog
 
+ * 0.4.6 (5 Dec 2017): Fix indexInMatch ([See #60](https://github.com/padolsey/findAndReplaceDOMText/issues/60)). Fix undefined being echoed in optional+empty capture groups ([See #70](https://github.com/padolsey/findAndReplaceDOMText/issues/70)).
  * 0.4.4 (4 May 2015): Remove duplicate key from `NON_CONTIGUOUS_PROSE_ELEMENTS`. Expose library via UMD ([See #32](https://github.com/padolsey/findAndReplaceDOMText/issues/32)).
  * 0.4.3 (28 Apr 2015): Add `preset:prose` and `forceContext` features. [See #29](https://github.com/padolsey/findAndReplaceDOMText/issues/29).
  * 0.4.2 (30 Mar 2014): Fix IE to avoid incorrectly-closed-tags issue ([see #20](https://github.com/padolsey/findAndReplaceDOMText/issues/20)). Thanks to [shauryamal](https://github.com/shauryamal)!
diff --git a/src/findAndReplaceDOMText.js b/src/findAndReplaceDOMText.js
index 556cc9a..f4c4cb9 100644
--- a/src/findAndReplaceDOMText.js
+++ b/src/findAndReplaceDOMText.js
@@ -1,5 +1,5 @@
 /**
- * findAndReplaceDOMText v 0.4.5
+ * findAndReplaceDOMText v 0.4.6
  * @author James Padolsey http://james.padolsey.com
  * @license http://unlicense.org/UNLICENSE
  *
@@ -334,14 +334,18 @@
 				if (curNode.nodeType === Node.TEXT_NODE) {
 
 					if (!endPortion && curNode.length + atIndex >= match.endIndex) {
-
 						// We've found the ending
+						// (Note that, in the case of a single portion, it'll be an
+						// endPortion, not a startPortion.)
 						endPortion = {
 							node: curNode,
 							index: portionIndex++,
 							text: curNode.data.substring(match.startIndex - atIndex, match.endIndex - atIndex),
-							indexInMatch: atIndex - match.startIndex,
-							indexInNode: match.startIndex - atIndex, // always zero for end-portions
+
+							// If it's the first match (atIndex==0) we should just return 0
+							indexInMatch: atIndex === 0 ? 0 : atIndex - match.startIndex,
+
+							indexInNode: match.startIndex - atIndex,
 							endIndexInNode: match.endIndex - atIndex,
 							isEnd: true
 						};
@@ -459,7 +463,7 @@
 						replacement = match.input.substring(match.endIndex);
 						break;
 					default:
-						replacement = match[+t];
+						replacement = match[+t] || '';
 				}
 				return replacement;
 			});
diff --git a/test/test.js b/test/test.js
index cf91132..0562d2f 100644
--- a/test/test.js
+++ b/test/test.js
@@ -328,6 +328,17 @@ test('Right (\')', function() {
 	htmlEqual(d.innerHTML, 'this is [ test] test');
 });
 
+test('Empty captured groups', function() {
+	var d = document.createElement('div');
+	d.innerHTML = '111333';
+	findAndReplaceDOMText(d, {
+		find: /(1+)(\s+)?(3+)/g,
+		replace: '$3$2$1'
+	});
+	// $2 is empty, so should be replaced by nothing (empty string):
+	htmlEqual(d.innerHTML, '333111');
+});
+
 module('Filtering');
 
 test('Element filtering', function() {
@@ -480,3 +491,44 @@ test('prose', function() {
 	');
 
 });
+
+module('indexInMatch');
+
+test('Single portion', function() {
+	var d = document.createElement('div');
+	d.innerHTML = '___AAAAA';
+	//                ^ 0
+	findAndReplaceDOMText(d, {
+		find: /A+/g,
+		replace: function(portion) {
+			return portion.indexInMatch;
+		}
+	});
+	htmlEqual(d.innerHTML, '___0');
+});
+
+test('Two portions', function() {
+	var d = document.createElement('div');
+	d.innerHTML = '___AAA<em>AA</em>';
+	//                ^ 0    ^ 3
+	findAndReplaceDOMText(d, {
+		find: /A+/g,
+		replace: function(portion) {
+			return portion.indexInMatch;
+		}
+	});
+	htmlEqual(d.innerHTML, '___0<em>3</em>');
+});
+
+test('>Two portions', function() {
+	var d = document.createElement('div');
+	d.innerHTML = '___AA<em>A</em>A<u>A</u>';
+	//                ^ 0   ^ 2   ^ 3 ^ 4
+	findAndReplaceDOMText(d, {
+		find: /A+/g,
+		replace: function(portion) {
+			return portion.indexInMatch;
+		}
+	});
+	htmlEqual(d.innerHTML, '___0<em>2</em>3<u>4</u>');
+});