diff --git a/lib/Slic3r/Surface.pm b/lib/Slic3r/Surface.pm
index 8ebddaa14..a3cbe4b08 100644
--- a/lib/Slic3r/Surface.pm
+++ b/lib/Slic3r/Surface.pm
@@ -93,10 +93,10 @@ sub p {
 sub is_solid {
     my $self = shift;
     my $type = $self->surface_type;
+    # S_TYPE_INTERNALBRIDGE is not solid because we can't merge it with other solid types
     return $type == S_TYPE_TOP
         || $type == S_TYPE_BOTTOM
-        || $type == S_TYPE_INTERNALSOLID
-        || $type == S_TYPE_INTERNALBRIDGE;
+        || $type == S_TYPE_INTERNALSOLID;
 }
 
 sub is_internal {