diff --git a/NEWS.md b/NEWS.md
index 5f2dd62cd..b4d9323ce 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -143,6 +143,8 @@ rowwiseDT(
 
 9. `key<-`, marked as deprecated since 2012 and unusable since v1.15.0, has been fully removed.
 
+10. Deprecation of `logicalAsInt` argument to `fwrite()` has been upgraded from a warning (since v1.15.0) to an error. It will be removed in the next release.
+
 # data.table [v1.16.2](https://github.com/Rdatatable/data.table/milestone/35) (9 October 2024)
 
 ## BUG FIXES
diff --git a/R/fwrite.R b/R/fwrite.R
index 6f40067c2..210f1d0bf 100644
--- a/R/fwrite.R
+++ b/R/fwrite.R
@@ -3,8 +3,8 @@ fwrite = function(x, file="", append=FALSE, quote="auto",
            sep2=c("","|",""), eol=if (.Platform$OS.type=="windows") "\r\n" else "\n",
            na="", dec=".", row.names=FALSE, col.names=TRUE,
            qmethod=c("double","escape"),
-           logical01=getOption("datatable.logical01", FALSE),
-           logicalAsInt=logical01,
+           logical01=getOption("datatable.logical01", FALSE), # due to change to TRUE; see NEWS
+           logicalAsInt=NULL,
            scipen=getOption('scipen', 0L),
            dateTimeAs = c("ISO","squash","epoch","write.csv"),
            buffMB=8, nThread=getDTthreads(verbose),
@@ -24,12 +24,8 @@ fwrite = function(x, file="", append=FALSE, quote="auto",
   else if (length(dateTimeAs)>1L) stopf("dateTimeAs must be a single string")
   dateTimeAs = chmatch(dateTimeAs, c("ISO","squash","epoch","write.csv"))-1L
   if (is.na(dateTimeAs)) stopf("dateTimeAs must be 'ISO','squash','epoch' or 'write.csv'")
-  if (!missing(logical01) && !missing(logicalAsInt))
-    stopf("logicalAsInt has been renamed logical01. Use logical01 only, not both.")
-  if (!missing(logicalAsInt)) {
-    warningf("logicalAsInt has been renamed logical01 for consistency with fread. It works fine for now but please change to logical01 at your convenience so we can remove logicalAsInt in future.")
-    logical01 = logicalAsInt
-    logicalAsInt=NULL
+  if (!is.null(logicalAsInt)) {
+    stopf("logicalAsInt has been renamed logical01 for consistency with fread.")
   }
   scipen = if (is.numeric(scipen)) as.integer(scipen) else 0L
   buffMB = as.integer(buffMB)
diff --git a/inst/tests/tests.Rraw b/inst/tests/tests.Rraw
index 39bce9730..c088474db 100644
--- a/inst/tests/tests.Rraw
+++ b/inst/tests/tests.Rraw
@@ -10933,10 +10933,7 @@ test(1736.03, fwrite(DT, sep2=c("",",","")), error="sep.*,.*sep2.*,.*must all be
 test(1736.04, fwrite(DT, sep2=c("","||","")), error="nchar.*sep2.*2")
 test(1736.05, capture.output(fwrite(DT, sep='|', sep2=c("c(",",",")"), logical01=FALSE)), c("A|B|C", "1|c(1,2,3,4,5,6,7,8,9,10)|c(s,t,u,v,w)",
  "2|c(15,16,17,18)|c(1.2,2.3,3.4,3.14159265358979,-9)", "3|c(7)|c(foo,bar)", "4|c(9,10)|c(TRUE,TRUE,FALSE)"))
-test(1736.06, capture.output(fwrite(DT, sep='|', sep2=c("{",",","}"), logicalAsInt=TRUE)),
- c("A|B|C", "1|{1,2,3,4,5,6,7,8,9,10}|{s,t,u,v,w}",
- "2|{15,16,17,18}|{1.2,2.3,3.4,3.14159265358979,-9}", "3|{7}|{foo,bar}", "4|{9,10}|{1,1,0}"),
- warning="logicalAsInt has been renamed logical01")
+test(1736.06, fwrite(DT, sep='|', sep2=c("{",",","}"), logicalAsInt=TRUE), error="logicalAsInt has been renamed logical01")
 DT = data.table(A=c("foo","ba|r","baz"))
 test(1736.07, capture.output(fwrite(DT,na="")), c("A","foo","ba|r","baz"))    # no list column so no need to quote
 test(1736.08, capture.output(fwrite(DT)), c("A","foo","ba|r","baz"))
@@ -15957,8 +15954,7 @@ DT[ , z := 0L]
 test(2074.31, dcast(DT, V1 ~ z, fun.aggregate=eval(quote(length)), value.var='z'),
      data.table(V1=c('a', 'b'), `0`=2:1,key='V1'))
 
-# fwrite both logical args
-test(2074.32, fwrite(DT, logical01=TRUE, logicalAsInt=TRUE), error="logicalAsInt has been renamed")
+# 2074.32 tested that setting both logical01 and logicalAsInt errored; no longer relevant
 
 # merge.data.table
 test(2074.33, merge(DT, DT, by.x = 1i, by.y=1i), error="A non-empty vector of column names is required")
diff --git a/man/fwrite.Rd b/man/fwrite.Rd
index ec23729c3..6cef5ec0a 100644
--- a/man/fwrite.Rd
+++ b/man/fwrite.Rd
@@ -11,8 +11,8 @@ fwrite(x, file = "", append = FALSE, quote = "auto",
   eol = if (.Platform$OS.type=="windows") "\r\n" else "\n",
   na = "", dec = ".", row.names = FALSE, col.names = TRUE,
   qmethod = c("double","escape"),
-  logical01 = getOption("datatable.logical01", FALSE),
-  logicalAsInt = logical01,  # deprecated
+  logical01 = getOption("datatable.logical01", FALSE),  # due to change to TRUE; see NEWS
+  logicalAsInt = NULL,  # deprecated
   scipen = getOption('scipen', 0L),
   dateTimeAs = c("ISO","squash","epoch","write.csv"),
   buffMB = 8L, nThread = getDTthreads(verbose),