diff --git a/avrdude/ChangeLog b/avrdude/ChangeLog
index d0bcf4a7..285983e6 100644
--- a/avrdude/ChangeLog
+++ b/avrdude/ChangeLog
@@ -1,3 +1,9 @@
+2009-07-02  Joerg Wunsch <j.gnu@uriah.heep.sax.de>
+
+	bug #22234: WINDOWS version: HOWTO: Specify Serial Ports Larger than COM9
+	* ser_win32.c (ser_open): prepend \\.\ to any COM port name, so it is
+	safe to be used for COM ports above 9.
+
 2009-07-02  Joerg Wunsch <j.gnu@uriah.heep.sax.de>
 
 	bug #26408: Crash in stk500v2_open()
diff --git a/avrdude/ser_win32.c b/avrdude/ser_win32.c
index aa4cc34c..ed8eb29d 100644
--- a/avrdude/ser_win32.c
+++ b/avrdude/ser_win32.c
@@ -110,6 +110,7 @@ static void ser_open(char * port, long baud, union filedescriptor *fdp)
 {
 	LPVOID lpMsgBuf;
 	HANDLE hComPort=INVALID_HANDLE_VALUE;
+	char *newname = 0;
 
 	/*
 	 * If the port is of the form "net:<host>:<port>", then
@@ -125,10 +126,22 @@ static void ser_open(char * port, long baud, union filedescriptor *fdp)
 		exit(1);
 	}
 
-	/* if (hComPort!=INVALID_HANDLE_VALUE) 
-		fprintf(stderr, "%s: ser_open(): \"%s\" is already open\n",
-				progname, port);
-	*/
+	if (strncasecmp(port, "com", strlen("com")) == 0) {
+
+	    // prepend "\\\\.\\" to name, required for port # >= 10
+	    newname = malloc(strlen("\\\\.\\") + strlen(port) + 1);
+
+	    if (newname == 0) {
+		fprintf(stderr,
+			"%s: ser_open(): out of memory\n",
+			progname);
+		exit(1);
+	    }
+	    strcpy(newname, "\\\\.\\");
+	    strcat(newname, port);
+
+	    port = newname;
+	}
 
 	hComPort = CreateFile(port, GENERIC_READ | GENERIC_WRITE, 0, NULL,
 		OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
@@ -174,6 +187,10 @@ static void ser_open(char * port, long baud, union filedescriptor *fdp)
 				progname, port);
 		exit(1);
 	}
+
+	if (newname != 0) {
+	    free(newname);
+	}
 }