diff --git a/android-chrome-192x192.png b/android-chrome-192x192.png
old mode 100755
new mode 100644
diff --git a/android-chrome-256x256.png b/android-chrome-256x256.png
old mode 100755
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diff --git a/apple-touch-icon.png b/apple-touch-icon.png
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diff --git a/assets/avatar/fathom-avatar.png b/assets/avatar/fathom-avatar.png
old mode 100755
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diff --git a/assets/avatar/favicon.png b/assets/avatar/favicon.png
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diff --git a/assets/avatar/og-image.jpg b/assets/avatar/og-image.jpg
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diff --git a/assets/avatar/subicon.png b/assets/avatar/subicon.png
old mode 100755
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diff --git a/browserconfig.xml b/browserconfig.xml
old mode 100755
new mode 100644
diff --git a/favicon-16x16.png b/favicon-16x16.png
old mode 100755
new mode 100644
diff --git a/favicon-32x32.png b/favicon-32x32.png
old mode 100755
new mode 100644
diff --git a/favicon.ico b/favicon.ico
old mode 100755
new mode 100644
diff --git a/favicon.png b/favicon.png
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new mode 100644
diff --git a/img/library-4785580_1920.jpg b/img/library-4785580_1920.jpg
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diff --git a/img/og-image.jpg b/img/og-image.jpg
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new mode 100644
diff --git a/index.php b/index.php
index 3e04e78..4b4cfe6 100644
--- a/index.php
+++ b/index.php
@@ -104,6 +104,12 @@
 						</label><span class="far fa-question-circle icon-sm" data-placement="right" data-toggle="tooltip" title="Search by author"></span>
 						<input id="author" name="author" class="form-control" placeholder="Gail Simone" />
 					</div>
+					<div class="form-group">
+						<label>
+							ISBN<br>
+						</label><span class="far fa-question-circle icon-sm" data-placement="right" data-toggle="tooltip" title="Search by ISBN"></span>
+						<input id="isbn" name="isbn" class="form-control" placeholder="9780441007462" />
+					</div>
 					<div class="form-group">
 						<label>
 							Call Number<br>
diff --git a/js/jqBootstrapValidation.js b/js/jqBootstrapValidation.js
old mode 100755
new mode 100644
diff --git a/js/lazysizes.min.js b/js/lazysizes.min.js
old mode 100755
new mode 100644
diff --git a/mstile-150x150.png b/mstile-150x150.png
old mode 100755
new mode 100644
diff --git a/safari-pinned-tab.svg b/safari-pinned-tab.svg
old mode 100755
new mode 100644
diff --git a/site.webmanifest b/site.webmanifest
old mode 100755
new mode 100644
diff --git a/yourlink.php b/yourlink.php
index 1cd2774..ee00694 100644
--- a/yourlink.php
+++ b/yourlink.php
@@ -21,6 +21,9 @@ $subject = filter_var($incomingsubject, FILTER_SANITIZE_STRING);
 $incomingauthor = $_POST['author'];
 $author = filter_var($incomingauthor, FILTER_SANITIZE_STRING);
 
+$incomingisbn = $_POST['isbn'];
+$isbn = filter_var($incomingisbn, FILTER_SANITIZE_STRING);
+
 $incomingcallno = $_POST['callnumber'];
 $callnumber = filter_var($incomingcallno, FILTER_SANITIZE_STRING);
 
@@ -56,6 +59,10 @@ if (!empty($author)) {
     $au = $searchjoiner.'au='.$author;
 }
 
+if (!empty($isbn)) {
+	$isbnum = $searchjoiner.'isbn='.$isbn;
+}
+
 if (!empty($callnumber)) {
     $call = $searchjoiner.'call='.$callnumber;
 }
@@ -79,7 +86,7 @@ if (!empty($title)) {
     $urlend = $searchsuffix;
 }
 
-$SearchURL = implode("", array_filter(array($url, $searchprefix, $ctx, $searchmiddle, $la, $au, $call, $kw, $su, $mat, $col, $tom, $urlend)));
+$SearchURL = implode("", array_filter(array($url, $searchprefix, $ctx, $searchmiddle, $la, $au, $isbnum, $call, $kw, $su, $mat, $col, $tom, $urlend)));
 
 ?>