diff --git a/rhodecode/templates/pullrequests/pullrequest.html b/rhodecode/templates/pullrequests/pullrequest.html
--- a/rhodecode/templates/pullrequests/pullrequest.html
+++ b/rhodecode/templates/pullrequests/pullrequest.html
@@ -107,6 +107,7 @@
                 <div class="reviewers-title block-right">
                     <div class="pr-details-title">
                         ${_('Pull request reviewers')}
+                        <span class="calculate-reviewers"> - ${_('loading...')}</span>
                     </div>
                 </div>
                 <div id="reviewers" class="block-right pr-details-content reviewers">
@@ -247,16 +248,33 @@
       query.callback({results: data.results});
   };
 
-  var prButtonLock = function(lockEnabled, msg) {
+
+  var prButtonLockChecks = {
+      'compare': false,
+      'reviewers': false
+  };
+
+  var prButtonLock = function(lockEnabled, msg, scope) {
+      scope = scope || 'all';
+      if (scope == 'all'){
+          prButtonLockChecks['compare'] = !lockEnabled;
+          prButtonLockChecks['reviewers'] = !lockEnabled;
+      } else if (scope == 'compare') {
+          prButtonLockChecks['compare'] = !lockEnabled;
+      } else if (scope == 'reviewers'){
+          prButtonLockChecks['reviewers'] = !lockEnabled;
+      }
+      var checksMeet = prButtonLockChecks.compare && prButtonLockChecks.reviewers;
       if (lockEnabled) {
           $('#save').attr('disabled', 'disabled');
       }
-      else {
+      else if (checksMeet) {
           $('#save').removeAttr('disabled');
       }
 
-      $('#pr_open_message').html(msg);
-
+      if (msg) {
+          $('#pr_open_message').html(msg);
+      }
   };
 
   var loadRepoRefDiffPreview = function() {
@@ -284,7 +302,7 @@
       var url = pyroutes.url('compare_url', url_data);
 
       // lock PR button, so we cannot send PR before it's calculated
-      prButtonLock(true, "${_('Loading compare ...')}");
+      prButtonLock(true, "${_('Loading compare ...')}", 'compare');
 
       if (loadRepoRefDiffPreview._currentRequest) {
           loadRepoRefDiffPreview._currentRequest.abort();
@@ -340,10 +358,10 @@
 
               if (commitElements.length) {
                   var commitsLink = '<a href="#pull_request_overview"><strong>{0}</strong></a>'.format(commitElements.length);
-                  prButtonLock(false, msg.replace('__COMMITS__', commitsLink));
+                  prButtonLock(false, msg.replace('__COMMITS__', commitsLink), 'compare');
               }
               else {
-                  prButtonLock(true, "${_('There are no commits to merge.')}");
+                  prButtonLock(true, "${_('There are no commits to merge.')}", 'compare');
               }
 
 
@@ -391,7 +409,7 @@
     var globalDefaults = {
         dropdownAutoWidth: true,
         containerCssClass: "drop-menu",
-        dropdownCssClass: "drop-menu-dropdown",
+        dropdownCssClass: "drop-menu-dropdown"
     };
 
     var initSelect2 = function(defaultOptions) {
@@ -422,7 +440,7 @@
         element.select2('val', defaultSourceRepo);
         if (readOnly === true) {
           element.select2('readonly', true);
-        };
+        }
       }
     };
   };
@@ -519,6 +537,9 @@
     if (loadDefaultReviewers._currentRequest) {
         loadDefaultReviewers._currentRequest.abort();
     }
+    $('.calculate-reviewers').show();
+    prButtonLock(true, null, 'reviewers');
+
     var url = pyroutes.url('repo_default_reviewers_data', {'repo_name': targetRepoName});
 
     var sourceRepo = $sourceRepo.eq(0).val();
@@ -531,7 +552,7 @@
     url += '&target_ref=' + targetRef[2];
 
     loadDefaultReviewers._currentRequest = $.get(url)
-          .done(function(data) {
+        .done(function(data) {
             loadDefaultReviewers._currentRequest = null;
 
             // reset && add the reviewer based on selected repo
@@ -543,9 +564,12 @@
                   reviewer.lastname, reviewer.username,
                   reviewer.gravatar_link, reviewer.reasons);
             }
-    });
+            $('.calculate-reviewers').hide();
+            prButtonLock(false, null, 'reviewers');
+        });
   };
-  prButtonLock(true, "${_('Please select origin and destination')}");
+
+  prButtonLock(true, "${_('Please select origin and destination')}", 'all');
 
   // auto-load on init, the target refs select2
   calculateContainerWidth();
@@ -555,12 +579,12 @@
       $(this).removeClass('autogenerated-title');
   });
 
-  %if c.default_source_ref:
+  % if c.default_source_ref:
       // in case we have a pre-selected value, use it now
       $sourceRef.select2('val', '${c.default_source_ref}');
       loadRepoRefDiffPreview();
       loadDefaultReviewers();
-  %endif
+  % endif
 
   ReviewerAutoComplete('user');
 });