--- a/lib/dirname.c
+++ b/lib/dirname.c
@@ -113,7 +113,7 @@
 	 canonicalized "d:/path", leave alone the root case "d:/".  */
       char const *lim = path + FILESYSTEM_PREFIX_LEN (path);
 
-      while (slash > lim && ISSLASH (*slash))
+      while (lim < slash && ISSLASH (*slash))
 	--slash;
 
       length = slash - path + 1;

--- a/lib/stripslash.c
+++ b/lib/stripslash.c
@@ -19,12 +19,16 @@
 # include <config.h>
 #endif
 
-#if defined(STDC_HEADERS) || defined(HAVE_STRING_H)
+#if STDC_HEADERS || HAVE_STRING_H
 # include <string.h>
 #else
 # include <strings.h>
 #endif
 
+#ifndef ISSLASH
+# define ISSLASH(C) ((C) == '/')
+#endif
+
 /* Remove trailing slashes from PATH.
    This is useful when using filename completion from a shell that
    adds a "/" after directory names (such as tcsh and bash), because
@@ -37,6 +41,6 @@
   int last;
 
   last = strlen (path) - 1;
-  while (last > 0 && path[last] == '/')
+  while (0 < last && ISSLASH (path[last]))
     path[last--] = '\0';
 }