diff --git a/C4/Context.pm b/C4/Context.pm
index 188a7ba27e..099ddaf6e6 100644
--- a/C4/Context.pm
+++ b/C4/Context.pm
@@ -604,6 +604,11 @@ sub set_preference {
 
     $value = 0 if ( $type && $type eq 'YesNo' && $value eq '' );
 
+    # force explicit protocol on OPACBaseURL
+    if ($var eq 'opacbaseurl' && substr($value,0,4) !~ /http/) {
+        $value = 'http://' . $value;
+    }
+
     if ($syspref) {
         $syspref = $syspref->set( { value => $value } )->store();
     }