diff --git a/R/data.table.R b/R/data.table.R
index e95420b6e0..ccb7f36e60 100644
--- a/R/data.table.R
+++ b/R/data.table.R
@@ -2261,7 +2261,7 @@ is.na.data.table = function (x) {
 Ops.data.table = function(e1, e2 = NULL)
 {
   ans = NextMethod()
-  if (cedta() && is.data.frame(ans)) ans = as.data.table(ans) 
+  if (cedta() && is.data.frame(ans)) ans = as.data.table(ans)
   else if (is.matrix(ans)) colnames(ans) = copy(colnames(ans))
   ans
 }
@@ -2358,7 +2358,10 @@ copy = function(x) {
       .Call(C_unlock, y)
       setalloccol(y)
     } else if (is.list(y)) {
+      oldClass = class(y)
+      setattr(y, 'class', NULL)  # otherwise [[.person method (which returns itself) results in infinite recursion, #4620
       y[] = lapply(y, reallocate)
+      if (!identical(oldClass, 'list')) setattr(y, 'class', oldClass)
     }
     y
   }
diff --git a/inst/tests/tests.Rraw b/inst/tests/tests.Rraw
index 774911872f..adaea569c6 100644
--- a/inst/tests/tests.Rraw
+++ b/inst/tests/tests.Rraw
@@ -17102,3 +17102,8 @@ options(old)
 # 1 is treated as . in dcast formula, #4615
 DT = data.table(a = c("s", "x"), survmean = 1:2)
 test(2151, dcast(DT, 1 ~ a, value.var='survmean'), data.table('.'='.', s=1L, x=2L, key='.'))
+
+# list object with [[ method that returns itself (e.g. person) lead to infinite loop in copy(), #4620
+y = person(given='Joel', family='Mossong')
+test(2152, copy(y), y)
+