diff --git a/winsup/cygwin/fhandler_serial.cc b/winsup/cygwin/fhandler_serial.cc
index 615b2513f..69e5768f6 100644
--- a/winsup/cygwin/fhandler_serial.cc
+++ b/winsup/cygwin/fhandler_serial.cc
@@ -519,14 +519,7 @@ fhandler_serial::ioctl (unsigned int cmd, void *buf)
 	  }
 	break;
      case TIOCINQ:
-       if (ev & CE_FRAME || ev & CE_IOE || ev & CE_OVERRUN || ev & CE_RXOVER
-	   || ev & CE_RXPARITY)
-	 {
-	   set_errno (EINVAL);	/* FIXME: Use correct errno */
-	   res = -1;
-	 }
-       else
-	 ipbuf = st.cbInQue;
+       ipbuf = st.cbInQue;
        break;
      case TIOCGWINSZ:
        ((struct winsize *) buf)->ws_row = 0;
diff --git a/winsup/cygwin/release/3.1.5 b/winsup/cygwin/release/3.1.5
index e34fdb88d..e567ecb32 100644
--- a/winsup/cygwin/release/3.1.5
+++ b/winsup/cygwin/release/3.1.5
@@ -9,3 +9,6 @@ Bug Fixes:
 - Fix a segfault when starting, e.g., mintty from a bash in a console
   running xterm emulation.
   Addresses: https://cygwin.com/ml/cygwin/2020-02/msg00197.html
+
+- Fix TIOCINQ to always return number of inbound chars if available.
+  Addresses: https://cygwin.com/ml/cygwin/2020-02/msg00258.html