diff --git a/Makefile b/Makefile
index 6cb6da1e23..769fdc793d 100644
--- a/Makefile
+++ b/Makefile
@@ -148,7 +148,7 @@ winnt-x86-64:
 	$(MAKE) winnt-finish
 
 winnt-finish:
-	cp misc/factor-cygwin.sh factor
+	cp misc/factor-cygwin.sh ./factor
 
 wince-arm:
 	$(MAKE) $(EXECUTABLE) CONFIG=vm/Config.windows.ce.arm
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
 }