diff --git a/NEWS.md b/NEWS.md
index 5505c4cbc..7ec502902 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -14,6 +14,8 @@
     # 2:
     ```
 
+2. `cedta()` now returns `FALSE` if `.datatable.aware = FALSE` is set in the calling environment, [#5654](https://github.com/Rdatatable/data.table/issues/5654).
+
 ## NOTES
 
 1. `transform` method for data.table sped up substantially when creating new columns on large tables. Thanks to @OfekShilon for the report and PR. The implemented solution was proposed by @ColeMiller1.
diff --git a/R/cedta.R b/R/cedta.R
index 51dc0e9dd..c5b32e740 100644
--- a/R/cedta.R
+++ b/R/cedta.R
@@ -22,6 +22,10 @@ cedta.pkgEvalsUserCode = c("gWidgetsWWW","statET","FastRWeb","slidify","rmarkdow
 #   package authors could set it using assignInNamespace and then not revert its value properly which would
 #   cause subsequent calls from other packages to fail.
 
+# .datatable.aware = TRUE or .datatable.aware = FALSE can also be set directly in the calling frame,
+# e.g. at the start of a particular function to make it data.table-aware in an otherwise unaware package
+# or vice versa.
+
 # nocov start: very hard to reach this within our test suite -- the call stack within a call generated by e.g. knitr
 # for loop, not any(vapply_1b(.)), to allow early exit
 .any_eval_calls_in_stack <- function() {
@@ -39,8 +43,8 @@ cedta.pkgEvalsUserCode = c("gWidgetsWWW","statET","FastRWeb","slidify","rmarkdow
 cedta = function(n=2L) {
   # Calling Environment Data Table Aware
   env = parent.frame(n)
-  if (isTRUE(env$.datatable.aware)) {  # dtplyr 184
-    return(TRUE)
+  if (isTRUEorFALSE(env$.datatable.aware)) { # dtplyr#184, #5654
+    return(env$.datatable.aware)
   }
   ns = topenv(env)
   if (!isNamespace(ns)) {
diff --git a/inst/tests/tests.Rraw b/inst/tests/tests.Rraw
index a5a7708bc..7e64bdc1a 100644
--- a/inst/tests/tests.Rraw
+++ b/inst/tests/tests.Rraw
@@ -18268,3 +18268,13 @@ test(2244.2, DT[, let(a=1, )], error="let.*Did you forget a trailing comma\\?")
 test(2244.3, DT[, `:=`(a=1, , b=2)], error="`:=`.*\\[2\\]")
 test(2244.4, DT[, let(a=1, , b=2)], error="let.*\\[2\\]")
 test(2244.5, DT[, `:=`(a=1, , b=2, )], error="[2, 4]")
+
+# allow specifying datatable-unaware behavior, #5654 / #5655
+dt = data.table(foo = 1:3, bar = 4:6)
+.datatable.aware = TRUE
+test(2245.1, dt[1], data.table(foo = 1L, bar = 4L)) # Single index should be interpreted as row
+.datatable.aware = FALSE
+# selfrefok() fails on unaware-indexed datatables; the copy() here sidesteps that issue.
+test(2245.2, copy(dt[1]), data.table(foo = 1:3)) # Revert to data.frame syntax: Interpret index as column
+rm(.datatable.aware)
+test(2245.3, dt[1], data.table(foo = 1L, bar = 4L)) # Default in this environment should be datatable-aware