diff --git a/tests/midline-flush.args b/tests/midline-flush.args
index f9cb27a..5097348 100644
--- a/tests/midline-flush.args
+++ b/tests/midline-flush.args
@@ -1 +1 @@
--- sh -c 'for i in `seq 1 10`; do tests/midline-flush; done'
+-- sh -c 'for i in `seq 1 10`; do tests/midline-flush $i; sleep 0.01; done'
diff --git a/tests/midline-flush.c b/tests/midline-flush.c
index 4166be3..719677c 100644
--- a/tests/midline-flush.c
+++ b/tests/midline-flush.c
@@ -7,10 +7,10 @@
 #include <stdio.h>
 #include <unistd.h>
 
-#define hello(fd) fprintf(fd, "Hello, %s! ", fd == stdout ? "stdout" : "stderr")
-#define goodbye(fd) fprintf(fd, "Goodbye, %s!\n", fd == stdout ? "stdout" : "stderr")
+#define hello(fd) fprintf(fd, "%s: Hello, %s! ", argv[1], fd == stdout ? "stdout" : "stderr")
+#define goodbye(fd) fprintf(fd, "%s: Goodbye, %s!\n", argv[1], fd == stdout ? "stdout" : "stderr")
 
-int main() {
+int main(int argc, char *argv[]) {
     hello(stdout);
     hello(stderr);
     fflush(stdout);
diff --git a/tests/midline-flush.err b/tests/midline-flush.err
index a677517..c63afac 100644
--- a/tests/midline-flush.err
+++ b/tests/midline-flush.err
@@ -1,10 +1,10 @@
-Hello, stderr! Goodbye, stderr!
-Hello, stderr! Goodbye, stderr!
-Hello, stderr! Goodbye, stderr!
-Hello, stderr! Goodbye, stderr!
-Hello, stderr! Goodbye, stderr!
-Hello, stderr! Goodbye, stderr!
-Hello, stderr! Goodbye, stderr!
-Hello, stderr! Goodbye, stderr!
-Hello, stderr! Goodbye, stderr!
-Hello, stderr! Goodbye, stderr!
+1: Hello, stderr! 1: Goodbye, stderr!
+2: Hello, stderr! 2: Goodbye, stderr!
+3: Hello, stderr! 3: Goodbye, stderr!
+4: Hello, stderr! 4: Goodbye, stderr!
+5: Hello, stderr! 5: Goodbye, stderr!
+6: Hello, stderr! 6: Goodbye, stderr!
+7: Hello, stderr! 7: Goodbye, stderr!
+8: Hello, stderr! 8: Goodbye, stderr!
+9: Hello, stderr! 9: Goodbye, stderr!
+10: Hello, stderr! 10: Goodbye, stderr!
diff --git a/tests/midline-flush.log b/tests/midline-flush.log
index 5da343b..a102224 100644
--- a/tests/midline-flush.log
+++ b/tests/midline-flush.log
@@ -1,20 +1,20 @@
-Hello, stderr! Goodbye, stderr!
-Hello, stdout! Goodbye, stdout!
-Hello, stderr! Goodbye, stderr!
-Hello, stdout! Goodbye, stdout!
-Hello, stderr! Goodbye, stderr!
-Hello, stdout! Goodbye, stdout!
-Hello, stderr! Goodbye, stderr!
-Hello, stdout! Goodbye, stdout!
-Hello, stderr! Goodbye, stderr!
-Hello, stdout! Goodbye, stdout!
-Hello, stderr! Goodbye, stderr!
-Hello, stdout! Goodbye, stdout!
-Hello, stderr! Goodbye, stderr!
-Hello, stdout! Goodbye, stdout!
-Hello, stderr! Goodbye, stderr!
-Hello, stdout! Goodbye, stdout!
-Hello, stderr! Goodbye, stderr!
-Hello, stdout! Goodbye, stdout!
-Hello, stderr! Goodbye, stderr!
-Hello, stdout! Goodbye, stdout!
+1: Hello, stderr! 1: Goodbye, stderr!
+1: Hello, stdout! 1: Goodbye, stdout!
+2: Hello, stderr! 2: Goodbye, stderr!
+2: Hello, stdout! 2: Goodbye, stdout!
+3: Hello, stderr! 3: Goodbye, stderr!
+3: Hello, stdout! 3: Goodbye, stdout!
+4: Hello, stderr! 4: Goodbye, stderr!
+4: Hello, stdout! 4: Goodbye, stdout!
+5: Hello, stderr! 5: Goodbye, stderr!
+5: Hello, stdout! 5: Goodbye, stdout!
+6: Hello, stderr! 6: Goodbye, stderr!
+6: Hello, stdout! 6: Goodbye, stdout!
+7: Hello, stderr! 7: Goodbye, stderr!
+7: Hello, stdout! 7: Goodbye, stdout!
+8: Hello, stderr! 8: Goodbye, stderr!
+8: Hello, stdout! 8: Goodbye, stdout!
+9: Hello, stderr! 9: Goodbye, stderr!
+9: Hello, stdout! 9: Goodbye, stdout!
+10: Hello, stderr! 10: Goodbye, stderr!
+10: Hello, stdout! 10: Goodbye, stdout!
diff --git a/tests/midline-flush.out b/tests/midline-flush.out
index 1d8bdd2..b449163 100644
--- a/tests/midline-flush.out
+++ b/tests/midline-flush.out
@@ -1,10 +1,10 @@
-Hello, stdout! Goodbye, stdout!
-Hello, stdout! Goodbye, stdout!
-Hello, stdout! Goodbye, stdout!
-Hello, stdout! Goodbye, stdout!
-Hello, stdout! Goodbye, stdout!
-Hello, stdout! Goodbye, stdout!
-Hello, stdout! Goodbye, stdout!
-Hello, stdout! Goodbye, stdout!
-Hello, stdout! Goodbye, stdout!
-Hello, stdout! Goodbye, stdout!
+1: Hello, stdout! 1: Goodbye, stdout!
+2: Hello, stdout! 2: Goodbye, stdout!
+3: Hello, stdout! 3: Goodbye, stdout!
+4: Hello, stdout! 4: Goodbye, stdout!
+5: Hello, stdout! 5: Goodbye, stdout!
+6: Hello, stdout! 6: Goodbye, stdout!
+7: Hello, stdout! 7: Goodbye, stdout!
+8: Hello, stdout! 8: Goodbye, stdout!
+9: Hello, stdout! 9: Goodbye, stdout!
+10: Hello, stdout! 10: Goodbye, stdout!