diff --git a/mozilla/xpcom/typelib/xpidl/xpidl.h b/mozilla/xpcom/typelib/xpidl/xpidl.h
index 70eefc6b59a..9ee2d326f95 100644
--- a/mozilla/xpcom/typelib/xpidl/xpidl.h
+++ b/mozilla/xpcom/typelib/xpidl/xpidl.h
@@ -154,6 +154,12 @@ xpidl_malloc(size_t nbytes);
 char *
 xpidl_strdup(const char *s);
 
+/*
+ * Return a pointer to the start of the base filename of path
+ */
+const char *
+xpidl_basename(const char * path);
+
 /*
  * Process an XPIDL node and its kids, if any.
  */
diff --git a/mozilla/xpcom/typelib/xpidl/xpidl_header.c b/mozilla/xpcom/typelib/xpidl/xpidl_header.c
index e025bb5876b..8e816913249 100644
--- a/mozilla/xpcom/typelib/xpidl/xpidl_header.c
+++ b/mozilla/xpcom/typelib/xpidl/xpidl_header.c
@@ -60,7 +60,7 @@ write_indent(FILE *outfile) {
 static gboolean
 header_prolog(TreeState *state)
 {
-    const char *define = g_basename(state->basename);
+    const char *define = xpidl_basename(state->basename);
     fprintf(state->file, "/*\n * DO NOT EDIT.  THIS FILE IS GENERATED FROM"
             " %s.idl\n */\n", state->basename);
     fprintf(state->file,
@@ -116,7 +116,7 @@ header_prolog(TreeState *state)
 static gboolean
 header_epilog(TreeState *state)
 {
-    const char *define = g_basename(state->basename);
+    const char *define = xpidl_basename(state->basename);
     fprintf(state->file, "\n#endif /* __gen_%s_h__ */\n", define);
     return TRUE;
 }
diff --git a/mozilla/xpcom/typelib/xpidl/xpidl_idl.c b/mozilla/xpcom/typelib/xpidl/xpidl_idl.c
index 62b9db0f692..135119e0398 100644
--- a/mozilla/xpcom/typelib/xpidl/xpidl_idl.c
+++ b/mozilla/xpcom/typelib/xpidl/xpidl_idl.c
@@ -733,21 +733,18 @@ xpidl_process_idl(char *filename, IncludePathEntry *include_path,
     if (strcmp(outname, "-")) {
         const char *fopen_mode;
         const char *out_basename;
-#if defined(XP_UNIX)
-        const char os_separator = '/';
-#elif defined(XP_WIN)
-        const char os_separator = '\\';
-#endif
 
         /* explicit_output_filename can't be true without a filename */
         if (explicit_output_filename) {
             real_outname = g_strdup(outname);
         } else {
-
+/* 
+ *This combination seems a little strange, what about OS/2?
+ * Assume it's some build issue
+ */
 #if defined(XP_UNIX) || defined(XP_WIN)
-            tmp = strrchr(outname, os_separator);
-            if (!file_basename && tmp) {
-                out_basename = tmp + 1;
+            if (!file_basename) {
+                out_basename = xpidl_basename(outname);
             } else {
                 out_basename = outname;
             }
diff --git a/mozilla/xpcom/typelib/xpidl/xpidl_util.c b/mozilla/xpcom/typelib/xpidl/xpidl_util.c
index 0c3776b8944..237c9e463ae 100644
--- a/mozilla/xpcom/typelib/xpidl/xpidl_util.c
+++ b/mozilla/xpcom/typelib/xpidl/xpidl_util.c
@@ -733,3 +733,23 @@ verify_interface_declaration(IDL_tree interface_tree)
     }
     return TRUE;
 }
+
+/*
+ * Return a pointer to the start of the base filename of path
+ */
+const char *
+xpidl_basename(const char * path)
+{
+    const char * result = g_basename(path);
+    /* 
+     *If this is windows then we'll handle either / or \ as a separator
+     * g_basename only handles \ for windows
+     */
+#if defined(XP_WIN32)
+    const char * slash = strrchr(path, '/');
+    /* If we found a slash and its after the current default OS separator */
+    if (slash != NULL && (slash > result))
+        result = slash + 1;
+#endif
+    return result;
+}