diff --git a/frontend_tests/node_tests/markdown.js b/frontend_tests/node_tests/markdown.js
index 883e1525f6..808e0ffd21 100644
--- a/frontend_tests/node_tests/markdown.js
+++ b/frontend_tests/node_tests/markdown.js
@@ -229,8 +229,15 @@ var bugdown_data = JSON.parse(fs.readFileSync(path.join(__dirname, '../../zerver
          expected: '<p><img alt=":poop:" class="emoji" src="/static/generated/emoji/images/emoji/unicode/1f4a9.png" title="poop"></p>'},
         {input: '\u{1f937}',
          expected: '<p>\u{1f937}</p>' },
+        // Test only those realm filters which don't return True for
+        // `contains_backend_only_syntax()`. Those which return True
+        // are tested separately.
         {input: 'This is a realm filter #1234 with text after it',
          expected: '<p>This is a realm filter <a href="https://trac.zulip.net/ticket/1234" target="_blank" title="https://trac.zulip.net/ticket/1234">#1234</a> with text after it</p>'},
+        {input: '#1234is not a realm filter.',
+         expected: '<p>#1234is not a realm filter.</p>'},
+        {input: 'A pattern written as #1234is not a realm filter.',
+         expected: '<p>A pattern written as #1234is not a realm filter.</p>'},
         {input: 'This is a realm filter with ZGROUP_123:45 groups',
          expected: '<p>This is a realm filter with <a href="https://zone_45.zulip.net/ticket/123" target="_blank" title="https://zone_45.zulip.net/ticket/123">ZGROUP_123:45</a> groups</p>'},
         {input: 'This is an !avatar(cordelia@zulip.com) of Cordelia Lear',
@@ -335,12 +342,22 @@ var bugdown_data = JSON.parse(fs.readFileSync(path.join(__dirname, '../../zerver
     assert(message.flags.indexOf('mentioned') === -1);
 }());
 
+(function test_backend_only_realm_filters() {
+    var backend_only_realm_filters = [
+        'Here is the PR-#123.',
+        'Function abc() was introduced in (PR)#123.',
+    ];
+    backend_only_realm_filters.forEach(function (content) {
+        assert.equal(markdown.contains_backend_only_syntax(content), true);
+    });
+}());
+
 (function test_python_to_js_filter() {
     // The only way to reach python_to_js_filter is indirectly, hence the call
     // to set_realm_filters.
     markdown.set_realm_filters([[ '/a(?im)a/g'], [ '/a(?L)a/g' ]]);
     var actual_value = (marked.InlineLexer.rules.zulip.realm_filters);
-    var expected_value = [ /\/aa\/g/gim, /\/aa\/g/g ];
+    var expected_value = [ /\/aa\/g(?![\w])/gim, /\/aa\/g(?![\w])/g ];
     assert.deepEqual(actual_value, expected_value);
 }());
 
diff --git a/static/js/markdown.js b/static/js/markdown.js
index 95ef63eb67..5e18ab5784 100644
--- a/static/js/markdown.js
+++ b/static/js/markdown.js
@@ -30,7 +30,16 @@ exports.contains_backend_only_syntax = function (content) {
     var markedup = _.find(backend_only_markdown_re, function (re) {
         return re.test(content);
     });
-    return markedup !== undefined;
+
+    // If a realm filter doesn't start with some specified characters
+    // then don't render it locally. It is workaround for the fact that
+    // javascript regex doesn't support lookbehind.
+    var false_filter_match = _.find(realm_filter_list, function (re) {
+        var pattern = /(?:[^\s'"\(,:<])/.source + re[0].source + /(?![\w])/.source;
+        var regex = new RegExp(pattern);
+        return regex.test(content);
+    });
+    return markedup !== undefined || false_filter_match !== undefined;
 };
 
 function push_uniquely(lst, elem) {
@@ -221,6 +230,15 @@ function python_to_js_filter(pattern, url) {
         });
         pattern = pattern.replace(inline_flag_re, "");
     }
+    // Ideally we should have been checking that realm filters
+    // begin with certain characters but since there is no
+    // support for negative lookbehind in javascript, we check
+    // for this condition in `contains_backend_only_syntax()`
+    // function. If the condition is satisfied then the message
+    // is rendered locally, otherwise, we return false there and
+    // message is rendered on the backend which has proper support
+    // for negative lookbehind.
+    pattern = pattern + /(?![\w])/.source;
     return [new RegExp(pattern, js_flags), url];
 }