diff --git a/build-support/factor.sh b/build-support/factor.sh
index b2b6ad1ff9..3517d8f4ba 100755
--- a/build-support/factor.sh
+++ b/build-support/factor.sh
@@ -236,7 +236,7 @@ find_word_size() {
 
 set_factor_binary() {
     case $OS in
-        winnt) FACTOR_BINARY=factor.exe;;
+        winnt) FACTOR_BINARY=factor.com;;
         *) FACTOR_BINARY=factor;;
     esac
 }