diff --git a/src/bin/pg_upgrade/test.sh b/src/bin/pg_upgrade/test.sh
index c9de4f8a7e..2d78f63f5e 100644
--- a/src/bin/pg_upgrade/test.sh
+++ b/src/bin/pg_upgrade/test.sh
@@ -244,8 +244,11 @@ esac
 
 pg_ctl start -l "$logdir/postmaster2.log" -o "$POSTMASTER_OPTS" -w
 
+# modern versions of msys/Windows require a double slash when calling
+# "cmd /c". This also works on older versions.
+
 case $testhost in
-	MINGW*)	cmd /c analyze_new_cluster.bat ;;
+	MINGW*)	cmd //c analyze_new_cluster.bat ;;
 	*)		sh ./analyze_new_cluster.sh ;;
 esac
 
@@ -258,7 +261,7 @@ if [ -n "$pg_dumpall2_status" ]; then
 fi
 
 case $testhost in
-	MINGW*)	cmd /c delete_old_cluster.bat ;;
+	MINGW*)	cmd //c delete_old_cluster.bat ;;
 	*)	    sh ./delete_old_cluster.sh ;;
 esac