diff --git a/DESCRIPTION b/DESCRIPTION
index 189ccd48d..a42e27d9a 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,7 +1,7 @@
 Package: collapse
 Title: Advanced and Fast Data Transformation
-Version: 2.0.17.9000
-Date: 2024-11-19
+Version: 2.0.18
+Date: 2024-11-23
 Authors@R: c(
            person("Sebastian", "Krantz", role = c("aut", "cre"), 
                   email = "sebastian.krantz@graduateinstitute.ch", 
diff --git a/NEWS.md b/NEWS.md
index 5cfdc2a5d..032c733f2 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,9 +1,11 @@
-# collapse 2.0.17.9000
+# collapse 2.0.18
 
 * Cases in `pivot(..., how = "longer")` with no `values` columns now no longer give an error. Thanks @alvarocombo for flagging this (#663).
 
 * Fixed bug in `qF(c(4L, 1L, NA), sort = FALSE)`: hash function failure due to a coding bug. Thanks @mayer79 for flagging this (#666).
 
+* If `x` is already a `qG` object of the right properties, calling `qG(x)` now does not copy `x` anymore. Thanks @mayer79 (https://github.com/mayer79/effectplots/issues/11).
+
 # collapse 2.0.17
 
 * In `GRP.default()`, the `"group.starts"` attribute is always returned, even if there is only one group or every observation is its own group. Thanks @JamesThompsonC (#631).  
diff --git a/R/GRP.R b/R/GRP.R
index c386ad000..18a686390 100644
--- a/R/GRP.R
+++ b/R/GRP.R
@@ -732,6 +732,7 @@ qG <- function(x, ordered = FALSE, na.exclude = TRUE, sort = .op[["sort"]],
         ax <- if(return.groups) list(N.groups = attr(x, "N.groups"), groups = attr(x, "groups"), class = newclx) else
           list(N.groups = attr(x, "N.groups"), class = newclx)
       }
+      if(identical(ax, attributes(x))) return(x)
       return(`attributes<-`(x, ax))
     }
     newclx <- c(if(ordered) "ordered", "qG", "na.included")
diff --git a/src/data.table_subset.c b/src/data.table_subset.c
index 02be2c3e5..d5d85ff0c 100644
--- a/src/data.table_subset.c
+++ b/src/data.table_subset.c
@@ -82,7 +82,9 @@ static SEXP shallow(SEXP dt, SEXP cols, R_len_t n)
   SEXP newdt = PROTECT(allocVector(VECSXP, n)); protecti++;   // to do, use growVector here?
   SET_ATTRIB(newdt, shallow_duplicate(ATTRIB(dt)));
   SET_OBJECT(newdt, OBJECT(dt));
-  if(IS_S4_OBJECT(dt)) newdt = asS4(newdt, TRUE, 1);  // To support S4 objects that include data.table
+  if(IS_S4_OBJECT(dt)) {
+    newdt = PROTECT(asS4(newdt, TRUE, 1)); protecti++;  // To support S4 objects that include data.table
+  }
   //SHALLOW_DUPLICATE_ATTRIB(newdt, dt);  // SHALLOW_DUPLICATE_ATTRIB would be a bit neater but is only available from R 3.3.0
 
   // TO DO: keepattr() would be faster, but can't because shallow isn't merely a shallow copy. It