diff --git a/NEWS.md b/NEWS.md
index 2d5ee8bbf7..34542e8a95 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -149,7 +149,7 @@
 
 26. `melt()` now outputs scalar logical `NA` instead of `NULL` in rows corresponding to missing list columns, for consistency with non-list columns when using `na.rm=TRUE`, [#5053](https://github.com/Rdatatable/data.table/pull/5053). Thanks to Toby Dylan Hocking for the PR.
 
-27. `as.data.frame(DT)` now removes any indices in addition to removing any key, [#5042](https://github.com/Rdatatable/data.table/issues/5042). When indices were left intact, a subsequent subset or reorder of the `data.frame` would not update the indices since they are treated just like any other `data.frame` attribute, causing incorrect results if the result is later converted back to `data.table` again.
+27. `as.data.frame(DT)`, `setDF(DT)` and `as.list(DT)` now remove the `"index"` attribute which contains any indices (a.k.a. secondary keys), as they already did for other `data.table`-only attributes such as the primary key stored in the `"sorted"` attribute. When indices were left intact, a subsequent subset or reorder of the `data.frame` by `data.frame`-code in base R or other packages would not update the indices, causing incorrect results if then converted back to `data.table`, [#4889](https://github.com/Rdatatable/data.table/issues/4889) [#5042](https://github.com/Rdatatable/data.table/issues/5042). Thanks @OfekShilon for the report and the PR.
 
 ## NOTES
 
diff --git a/R/data.table.R b/R/data.table.R
index c15d65f034..0a5a38785b 100644
--- a/R/data.table.R
+++ b/R/data.table.R
@@ -2140,7 +2140,7 @@ as.data.frame.data.table = function(x, ...)
   setattr(ans,"row.names",.set_row_names(nrow(x)))   # since R 2.4.0, data.frames can have non-character row names
   setattr(ans,"class","data.frame")
   setattr(ans,"sorted",NULL)  # remove so if you convert to df, do something, and convert back, it is not sorted
-  setattr(ans,"index",NULL) #5042
+  setattr(ans,"index",NULL)  #4889 #5042
   setattr(ans,".internal.selfref",NULL)
   # leave tl intact, no harm,
   ans
@@ -2157,6 +2157,7 @@ as.list.data.table = function(x, ...) {
   setattr(ans, "class", NULL)
   setattr(ans, "row.names", NULL)
   setattr(ans, "sorted", NULL)
+  setattr(ans, "index", NULL)  #4889 #5042
   setattr(ans,".internal.selfref", NULL)   # needed to pass S4 tests for example
   ans
 }
@@ -2716,6 +2717,7 @@ setDF = function(x, rownames=NULL) {
     setattr(x, "row.names", rn)
     setattr(x, "class", "data.frame")
     setattr(x, "sorted", NULL)
+    setattr(x, "index", NULL)  #4889 #5042
     setattr(x, ".internal.selfref", NULL)
   } else if (is.data.frame(x)) {
     if (!is.null(rownames)) {
diff --git a/inst/tests/tests.Rraw b/inst/tests/tests.Rraw
index aa654a236c..b6093cf9cd 100644
--- a/inst/tests/tests.Rraw
+++ b/inst/tests/tests.Rraw
@@ -17802,3 +17802,11 @@ test(2199.1, as.data.table(as.list(1:2))[, .SD,.SDcols=(-1L)],   data.table(V2=2
 test(2199.2, as.data.table(as.list(1:2))[, .SD,.SDcols=(-(1L))], data.table(V2=2L))
 test(2199.3, as.data.table(as.list(1:3))[, .SD,.SDcols=(-1L)],   data.table(V2=2L, V3=3L))
 test(2199.4, data.table(V1=-1L, V2=-2L, V3=-3L)[,.SD,.SDcols=-V2:-V1], error="not found")
+
+# setDF now drops index attributes, #4889
+d = data.table(a=1:100, b=1:100)
+setindex(d, a)
+setDF(d)
+d[1:50, "a"] = d[51:100, "a"]
+setDT(d)
+test(2200, nrow(d[a==99]), 2L)
diff --git a/man/setDF.Rd b/man/setDF.Rd
index f50c9ae491..57cba39433 100644
--- a/man/setDF.Rd
+++ b/man/setDF.Rd
@@ -15,7 +15,7 @@ setDF(x, rownames=NULL)
 }
 
 \details{
-  All \code{data.table} attributes including any keys of the input data.table are stripped off.
+  All \code{data.table} attributes including any keys and indices of the input data.table are stripped off.
 
   When using \code{rownames}, recall that the row names of a \code{data.frame} must be unique. By default, the assigned set of row names is simply the sequence 1, \ldots, \code{nrow(x)} (or \code{length(x)} for \code{list}s).
 }
diff --git a/src/utils.c b/src/utils.c
index 0c4f04fa39..a1d9093b8d 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -381,11 +381,11 @@ SEXP coerceAs(SEXP x, SEXP as, SEXP copyArg) {
 #include <zlib.h>
 #endif
 SEXP dt_zlib_version() {
-  char out[51];
+  char out[71];
 #ifndef NOZLIB
-  snprintf(out, 50, "zlibVersion()==%s ZLIB_VERSION==%s", zlibVersion(), ZLIB_VERSION);
+  snprintf(out, 70, "zlibVersion()==%s ZLIB_VERSION==%s", zlibVersion(), ZLIB_VERSION);
 #else
-  snprintf(out, 50, _("zlib header files were not found when data.table was compiled"));
+  snprintf(out, 70, _("zlib header files were not found when data.table was compiled"));
 #endif
   return ScalarString(mkChar(out));
 }