diff --git a/lib/system.nim b/lib/system.nim
index bab5369f11..6388e278e1 100644
--- a/lib/system.nim
+++ b/lib/system.nim
@@ -2743,6 +2743,7 @@ when not defined(JS): #and not defined(nimscript):
       # we use binary mode on Windows:
       c_setmode(c_fileno(stdin), O_BINARY)
       c_setmode(c_fileno(stdout), O_BINARY)
+      c_setmode(c_fileno(stderr), O_BINARY)
 
     when defined(endb):
       proc endbStep()
diff --git a/tests/osproc/ta.nim b/tests/osproc/ta.nim
deleted file mode 100644
index 5ebcc7f142..0000000000
--- a/tests/osproc/ta.nim
+++ /dev/null
@@ -1,3 +0,0 @@
-import strutils
-let x = stdin.readLine()
-echo x.parseInt + 5
diff --git a/tests/osproc/ta_in.nim b/tests/osproc/ta_in.nim
new file mode 100644
index 0000000000..b46890f6ea
--- /dev/null
+++ b/tests/osproc/ta_in.nim
@@ -0,0 +1,5 @@
+# This file is prefixed with an "a", because other tests
+# depend on it and it must be compiled first.
+import strutils
+let x = stdin.readLine()
+echo x.parseInt + 5
diff --git a/tests/osproc/ta_out.nim b/tests/osproc/ta_out.nim
new file mode 100644
index 0000000000..f7091a7f6a
--- /dev/null
+++ b/tests/osproc/ta_out.nim
@@ -0,0 +1,16 @@
+# This file is prefixed with an "a", because other tests
+# depend on it and it must be compiled first.
+stdout.writeLine("to stdout")
+stdout.flushFile()
+stdout.writeLine("to stdout")
+stdout.flushFile()
+
+stderr.writeLine("to stderr")
+stderr.flushFile()
+stderr.writeLine("to stderr")
+stderr.flushFile()
+
+stdout.writeLine("to stdout")
+stdout.flushFile()
+stdout.writeLine("to stdout")
+stdout.flushFile()
diff --git a/tests/osproc/tstdin.nim b/tests/osproc/tstdin.nim
index b491c25000..d94c34192d 100644
--- a/tests/osproc/tstdin.nim
+++ b/tests/osproc/tstdin.nim
@@ -4,7 +4,7 @@ discard """
 """
 import osproc, os, streams
 
-const filename = when defined(Windows): "ta.exe" else: "ta"
+const filename = when defined(Windows): "ta_in.exe" else: "ta_in"
 
 doAssert fileExists(getCurrentDir() / "tests" / "osproc" / filename)
 
diff --git a/tests/osproc/tstdout.nim b/tests/osproc/tstdout.nim
new file mode 100644
index 0000000000..0cb5bd9c08
--- /dev/null
+++ b/tests/osproc/tstdout.nim
@@ -0,0 +1,29 @@
+discard """
+  output: '''--------------------------------------
+to stdout
+to stdout
+to stderr
+to stderr
+to stdout
+to stdout
+--------------------------------------
+'''
+"""
+import osproc, os, streams
+
+const filename = when defined(Windows): "ta_out.exe" else: "ta_out"
+
+doAssert fileExists(getCurrentDir() / "tests" / "osproc" / filename)
+
+var p = startProcess(filename, getCurrentDir() / "tests" / "osproc",
+                     options={poStdErrToStdOut})
+
+let outputStream = p.outputStream
+var x = newStringOfCap(120)
+var output = ""
+while outputStream.readLine(x.TaintedString):
+  output.add(x & "\n")
+
+echo "--------------------------------------"
+stdout.write output
+echo "--------------------------------------"