Index: Doc/lib/libos.tex
===================================================================
--- Doc/lib/libos.tex	(revision 51868)
+++ Doc/lib/libos.tex	(working copy)
@@ -366,6 +366,10 @@
   \cfunction{_popen()} function from the libraries provided with
   Windows.  Newer versions of Python do not use the broken
   implementation from the Windows libraries]{2.0}
+\versionchanged[Earlier versions would run the string directly
+with cmd.exe /c on Windows. It now adds a pair of quotes around
+the command line string, to support cases where the command
+line string already contains multiple pairs of quotes]{2.6}
 \end{funcdesc}
 
 \begin{funcdesc}{tmpfile}{}
Index: Modules/posixmodule.c
===================================================================
--- Modules/posixmodule.c	(revision 51868)
+++ Modules/posixmodule.c	(working copy)
@@ -4633,10 +4633,10 @@
 		if (GetVersion() < 0x80000000 &&
 		    _stricmp(comshell, "command.com") != 0) {
 			/* NT/2000 and not using command.com. */
-			x = i + strlen(s3) + strlen(cmdstring) + 1;
+			x = i + strlen(s3) + strlen(cmdstring) + 3;
 			s2 = (char *)alloca(x);
 			ZeroMemory(s2, x);
-			PyOS_snprintf(s2, x, "%s%s%s", s1, s3, cmdstring);
+			PyOS_snprintf(s2, x, "%s%s\"%s\"", s1, s3, cmdstring);
 		}
 		else {
 			/*