Index: fdi.c
===================================================================
--- dll/win32/cabinet/fdi.c	(revision 73222)
+++ dll/win32/cabinet/fdi.c	(working copy)
@@ -2039,11 +2039,13 @@
             fullpath[0] = '\0';
             if (pathlen) {
               strcpy(fullpath, userpath);
-              if (fullpath[pathlen - 1] != '\\')
-                strcat(fullpath, "\\");
+              if (fullpath[pathlen - 1] == '\\')
+                fullpath[pathlen - 1] = '\0';
             }
-            if (filenamelen)
+            if (filenamelen) {
+              strcat(fullpath, "\\");
               strcat(fullpath, cab->mii.nextname);
+            }
 
             TRACE("full cab path/file name: %s\n", debugstr_a(fullpath));